36 Dr. Karl Krapelln on the Pulicidse. 
V. — On the Systematic Position of the Pulicidas. 
By Dr. Karl Krapelin*. 
[Plate ni.] 
After my investigations on the buccal organs of the Diptera 
and Rhynchota + had led me to the conclusion that in the 
former the true sucking-tube (not to be confounded with the 
labium, which serves only as its sheath) was formed by a 
dorsal and a ventral half-gutter (labrum and hypopharynx), 
and in the latter by two double half-gutters laterally inter- 
locked, it seemed natural to study also the aberrant members 
of the two series in the light of this criterion, which ap])lied 
to all typical forms, in order to arrive at greater clearness 
with regard to their relationships. In this respect no small 
interest undoubtedly attaches to the group Pulicidffi, which, 
notwithstanding much difference of form, presents such a 
uniformity of organization, and as to the systematic position 
of which for more than a century the most different opinions 
have been expressed, without any generally acceptable and 
well-established view having yet been arrived at. 
The history of these opinions has ah-eady been given 
pretty completely by Taschenberg in his Monograph on the 
Fleas J, so that here a short recapitulation may suffice. 
Linn^, as is well known, created an order Aptera for the 
wingless insects, Myriopods, Spiders, &c., and in this the flea 
found its place. A simihar position was assigned to it by 
Geoffroy, Cuvier, and Dumdril, as also by Gervais ; while, on 
the other hand, the order Aptera was by many rejected as 
unnatural, and the relationship of the Pulicidse with various 
winged insects was asserted. Thus Kircher referred them to 
the Orthoptera, Fabricius and Illiger to the E-hynchota, Rosel, 
Oken, Strauss-Durckheim, Newman, Burmeister, Walker, 
Von Siebold, and others to the Diptera. Lastly, there were 
also very early naturalists who would associate the flea with 
none of the existing orders of insects, but postulated a distinct 
order for it. The leader in this direction is De Geer. He 
was followed by Lamarck, Latreille, Kirby and Spence, 
MacLeay, Leach, Dug^s^ Bouchd, and Van der Hoeven, and, 
* ' Festschrift zum 50-jaliiigen Jiibiliium des Realgymnasiums des 
Jolianneiims,' Hamburg, 1884. Translated by AV, S. Dallas, F.L.S, 
+ In part set forth in the preliminaiy communication "Ueber dio. 
Mund-werkzeuge der saugenden Insekten" (Zool. Anz. 1882, pp. 674-79) 
and in a memoir, "Zur Anatomie und Physiologie des Eiissels voii 
Musca " (Zeitschr. f. wiss. Zool. xxxix. pp. 683-719). 
X Taschenberg, 'Die Flohe ' (Halle, 1880). 
Dr. Karl Krapelln on the Pdiclclae. 37 
among later investigators, by Landois and Tasclienberg. 
But although the last two authors especially pronounced most 
decidedly in favour of the independent position of the Fleas in 
the system, and although the most accepted special works 
upon the Diptera exclude the Fleas as not belonging to the 
series of forms in that order *, we find that even in the most 
recent manuals of zoology the group of insects in question is 
almost without exception cited as a suborder of the Diptera. 
This may pass in the first place as a proof that really stringent 
arguments have not yet been brought forward in favour of 
either view ; but we might also derive the hesitation felt by 
many zoologists to raise the rank of the Fleas (even under 
otherwise sufficient grounds) from the circumstance that they 
lead a parasitic existence, and by this means have possibly 
undergone profound and peculiar morphological changes by 
" adaptation," as is sufficiently established for other groups of 
parasitic forms. In opposition to this, however, it must be 
remembered that with only isolated exceptions (the females of 
the Sarcopsyllidffi) the Pulicidee are not stationary, but only 
temporary parasites, that their whole development is completed 
without parasitism, and that therefore we cannot well assume 
any considerable adaptation to a parasitic mode of life. But 
if this be so, if we succeed in proving that the Pulicidai possess 
a series of morphological characters which cannot be regarded 
as acquired by parasitism, we must necessarily, in judging of 
their position in the system, consider the same points of view 
to be prescriptive that have been generally adopted for the 
establishment of orders, suborders, and families in the class of 
insects. 
These general points of view, however, do not offer us a 
very brilliant prospect. The Linnean principium divisionisj 
the form, number, and texture of the wings, having proved to 
be untenable, we find on the one hand the kind of transforma- 
tion and its various stages, and on the othei the structure of the 
organs of the mouth, raised into the most important criteria 
of the nearer or more distant relationship of the groups of 
insects. But, as is always the case, when a single character 
is thrown too much into the foreground, and the general 
morphological relations of the two series of forms are not 
allowed to be prescriptive, difficulties make their appearance 
even with these apparently so thorough-going principles of 
division, which considerably diminish their value. The 
* It is interesting that the well-known work on the Diptera of the 
' Fauna Austriaca ' by Schiuer certainly expresses itself decidedly enough 
in the above sense, but then gives a detinition of the true Diptera, which 
might very well embrace the Pulicidae. 
38' Dr. Karl Krapelin on the Pulicidss. 
group of the Orthoptera, which is certainly not very natural, 
and their multifarious relations with the Neuroptera, the suc- 
torial ApidfB, the biting Mallophaga, and lastly the pupal 
rest of the male Coccidaj, may sufficiently establish this pro- 
position. It is still worse, however, as regards general avail- 
ability, with the distinctive characters of the orders generally 
cited — the segmentation of the thorax and tarsi, the structure of 
tlie wings, of the different buccal organs, antennae, &c. The 
mere fact of the agreement or difference of these organs individu- 
ally cannot give us certainty as to the systematic relationship 
of two series of forms, but only the examination whether the 
general organization of one group, as expressed in the deve- 
lopment of all morphological characters, shows or does not 
b\\ow jjhyhgenetic relations with those of another group; in 
other words, whether the observed ditterences in the structure 
of the parts may be referred equally v/ell to a different '' fun- 
damental plan " in their arrangement, as to simple changes of 
form and reductions, such as may be explained by altered 
function. Self-evident as this proposition appears in the 
light of modern zoology, the history of opinion as to the sys- 
tematic position of the flea nevertheless shows very plainly 
how little it has hitherto been taken into consideration by 
entomologists. One important aid in such investigations 
upon the true phylogenetie relationships of forms is unfortu- 
nately at present still almost wholly shut out from us. I refer 
to the anatomical structure of the organs. The knowledge of 
this, and especially that of the generative organs, is at present 
60 imperfect that a detailed consideration of the internal 
organization seems to be of little use in the classification of 
insects. 
After these prefatory remarks upon the principles which are 
or should be of force in the grouping of insect-forms, the 
question as to the systematic position of the Pulicidse may be 
postulated as follows : — Do they or do they not, in the totality 
of their organs, show near relations of affinity with any of the 
other groups of insects ? In the former case we should have 
to arrange them in this group of insects ; in the latter we 
must establish an independent order for them. 
I naturally commence my examination with that order of 
insects which, in the judgment of zoologists, has the most 
right to receive the Pulicidse into it, namely the Diptera. 
The series of the Diptera must decidedly be called a unitary 
one ; but the two characters so often brought prominently 
forward (a perfect metamorphosis and suctorial buccal organs) 
do not alone establish this unity, seeing that we must also 
ascribe them to the Lepidoptera, the Apid^, and the male 
Dr. Karl Krapelin on the Pulicidae. 39 
Coccidffi. Nay, even if we add the footless larvee and the 
fusion of the thoracic segments as further criteria, we might 
perfectly well unite the Bees with the Diptera. It is not the 
simple fact of the suctorial buccal organs that is of importance, 
hut their specific structure, the position and arrangement of 
the parts composing the suctorial apparatus. If we fix our 
attention upon this point we at once recognize that the fly's 
proboscis is constructed upon a perfectly different fundamental 
plan from that of the Apidee, that the two are not directly 
phylogenetically referable to each other, but that, on the 
other hand, the great variations in the buccal apparatus of the 
Diptera only represent modifications of one and the same 
type, distinctly demonstrable throughout. The characteristic 
of the bee's trunk consists in the development of the loivar 
parts of the mouth into the sucking organ, while the man- 
dibles retain their original function ; that of the fly's pro- 
boscis, on the contrary, in the employment of the labrum and 
hypopharynx for the formation of the sucking-tube, with 
which the mandibles and maxillae associate themselves as 
St} lets more or less developed as required, while at the same 
time the labium in all cases has to form a protective sheath 
for the comparatively delicate tube through which the fluids 
ascend. Tliis fundamental plan of the employment of the 
parts of the mouth occurs, as already pointed out in the 
introduction, in all the groups (except the Pulicidte) which 
have hitherto been placed in the group Diptera, in the piercing 
Culicidffi, Tabanidse, and Asilidas, the difterent families of 
honey-suckers, and the Pupipara, which are so depressed in 
position through parasitism ; nay, a bridge seems even to be 
thrown over towards the rudimentary buccal organs of the 
CEstridee, through the structures which occur in Gutereh^a. In 
figs. 1-3 (PI. III.) I have drawn transverse sections of the pro- 
boscides of those groups of flies which, upon one hand or the 
other, have been referred to as allied to the flea. While those 
of Tabanus and Gulex (figs. 1 and 3) agree not only in the 
position but also in the number of the pieces composing the 
proboscis, that of Melojyhagus (fig. 2, the representative of the 
Pupipara) shows a great reduction, which finds its expression 
in the entire absence of the mandibles and maxillas* ; but 
* The two valves embracing tlie proboscis of the Pupipara have 
been very erroneously interpreted as maxilla3, their palpi, or even 
as a bipartite epi pharynx (Meinert). From the whole arrangement of 
the proboscis, wliich is freely movable in a wide cavity of the head 
extending as far as the prothoracic ring, we can here have to do only 
with a conical prolongation of the head which has become paired, some- 
what such as we should obtain if we imagined the slight emargination 
at the apex of the frontal cone of Hhingia carried down to its base. The 
strongly projecting cheeks of many Conopidte might also perhaps bo 
regarded as analogous, 
40 Dr. Karl Kriipelin on the Pulicidae. 
nevertheless it is easy even here to recognize the typical 
position of the pieces forming the sucking-tube (dorsallythe 
labrum and ventrally the hypopharynx) , and the labium 
which encloses these as a sheath. _ Further, the latter bears 
at the end that enlarged portion which is so characteristic of 
all Diptera, and which is probably to be interpreted as formed 
by uniarticulate labial palpi. 
The same unity in the Diptera appears also in the special 
structure of the thorax and its appendages. That this appears 
always separated from the head by a deep incision is cer- 
tainly not without significance ; but it can furnish no decisive 
datum for the collocation of the Diptera. Of more importance, 
no doubt, is the fusion of the thoracic segments into a compact 
thoracic mass, which occurs in all the forms referred to this 
group. It is indeed true that in orders of insects (I refer 
particularly to the llhynchota) the formation of the thorax 
as regards the separation or fusion of the segments composing 
it shows manifold differences, without its being necessary that 
we should separate forms which are united for other reasons, 
seeing that the fusion or separation of the thoracic segments 
has to do essentially with a function of the mechanism of 
flight, and the free segmentation of the thorax in a wingless 
form may very well be explained as a correlative phenomenon 
of adaptation. But the conditions are different if, on the 
contrary, a wingless form exhibits complete amalgamation of 
the tlioracic segments. In my judgment it thereby demon- 
strates most unmistakably its descent from winged insects, 
and in this sense the compact structure of the thorax, with 
the characteristic process of the mesothorax described as the 
*• scutellum," in Aklophagus^ the Nycteribiidag, and the Brau- 
lida3, decidedly acquires the significance of a still uneffaced 
relationship with the winged groups standing next to them. 
And just as on account of this character tlie assumption is 
justified that the forms just mentioned stand in close phylo- 
genetic r.-lationship with winged insects, so does the ex- 
amination of the dorsal a])pendages of the thorax lead to tlie 
same conclusion. All Diptera do not possess a pair of 
wings and a pair of halteres ; but the two organs which, 
because special, are certainly of such great importance in 
characterizing the Diptera, disappear so gradually in the 
continuous series of forms, that we may trace their progress 
to the rudimentary state, as it were, step by step. An 
Ornithohia pallida which, as Lipoptena cervi, follows a per- 
fectly different mode of life, enables us at once to understand 
the case, when we see Melophngus, which is never parasitic 
upon birds, entirely destitute of wings. But as regards the 
Dr. Karl Krapelin oyi the Pulicldse. 41 
halteres, these, notwitlistancling Scliiner's assertion to the 
contrary, are quite recognizable in the sheep-tick, wliile in the 
Nycteribiida3 they show all gradations down to quite minute 
points, so that the complete absence of these apparently insig- 
nificant organs in the Braulldas need not give us any further 
disturbance. The ventral thoracic appendages, the legs, cer- 
tainly present but few differences in the group of the Diptera, 
nevertheless the five tarsal joints which are usually present 
are not always constant ; and further, other orders of insects 
sufficiently prove how little importance attaches in general to 
the number of tarsal joints and the development of the different 
sections of the legs. 
The developjnental stages of the Diptera do not show a 
community of type so distinctly as the structural characters 
just referred to. The larva? are certainly throughout distin- 
guished by the absence of jointed thoracic limbs, which is of 
special interest in the case of those forms which live free upon 
leaves by prey (many larvaa of Syrphidaj) ; but witli regard 
to the structure of the head, the armature of jaws, and the 
development of the traclieal system, there are, as is well 
known, such important differences, that they have been 
successfully employed for the systematic division of the order 
into several suborders and sections. Nevertheless even here 
intermediate grades are not wanting between the different 
structural characters (witness the variable development of the 
first cephalic segment) ; nay, in Brauer's* opinion, the family 
Lonchopteridas may possibly prove to be a perfect transitional 
group between the Orthorapha and Cyclorapha, so that the 
multifarious forms of the larvffi at least offer no veto against 
the unitariness of the stem of the Diptera. The same thing can 
also be said of the pupo3, which indeed likewise fall under two 
main types, but are so far brought together by Brauer's inves- 
tigations, that these furnish a proof that the so-called " tun- 
pupa?" (obtected pupee) show very different grades of structure, 
and in many of them the enveloping larva- skin bursts exactly 
as in the ordinary moulting, and consequently is to be referred 
simply to a delayed moulting at the close of the larval period. 
In the latter case, moreover, if the appendages of the segments 
of the body are not so closely attached to each other and to 
the body as in the naked and consequently less protected and 
more easily injured " mummy-pupa3," no important objection 
against the natural relationship of the two groups can be 
derived from this circumstance, which evidently results from 
* F. Brauer, ' Die Zweifliigler des Kais. Museums in Wien,' p. 9 
(Vienna, 1883) ; also iu the Ueulischr. d, math.-naturwiss. lilasse d. 
k.-k. Akad. d. Wiss. Bd. xlvii. 
42 Dr. Karl Krapelin on the Pulicidge. 
altered condition. The " mummy-pupEe," however, show- 
many differences amono- themselves with regard to the closer 
or looser appression of the appendages of the body, as may 
be demonstrated by a comparison of the pupee of the Asilidaj, 
which rest in the ground, and those of Tipulce which live in 
the water. 
Of anatomical peculiarities of the Diptera especial mention 
must be made of the " sucking-stomach," which is always 
present, as also of the large thoracic salivary glands, the 
eft'erent ducts of which, wherever the buccal organs perform 
any function, unite into an unpaired closed canal, which, 
running along in the cavity of the hypopharynx, opens at its 
extremity. The testes are almost always two ; the Malpi- 
ghian vessels almost as regularly four. As regards the 
tracheal system, the constant absence of the first thoracic 
stigma and the small number of abdominal stigmata are to 
be noticed ; while the nervous system, as is Avell known, 
shows all possible forms of development, from the most ex- 
treme concentration to a very considerable segmentation of the 
ganglionic chain. 
If Ave turn from this brief account of the Dipterous type to 
the characters of the Pulicida3, we must admit, in the first 
place, that in a whole series of points of comparison an agree- 
ment between the Diptera and the Fleas can be demonstrated. 
Like the Diptera, the Fleas have a suctorial buccal apparatus, 
a perfect metamorphosis, and footless larvee ; as in them also 
the tarsi are five-jointed, there are four Malpighian vessels, 
and one pair of testes. But, as has already been indicated at 
page 38, we could only ascribe decisive weight to this agree- 
ment if all these characters were peculiar to the Dipterous stem 
alone, and if at the same time, by more detailed comparison, 
real tenable parallels could be drawn between the different 
parts of the organs, as between the different stages of develop- 
ment. This, however, is by no means the case. The number 
of Malpighian vessels and of testes recurs in the same way in 
the Rhynchota, and therefore proves no more in favour of the 
relationship between the Fleas and the Diptera than the 
number of the tarsal joints or the annulation of the terminal 
knob of the autennce, which may be recognized in all possible 
groups of msects. At the first glance more importance seems 
to attach to the agreement of the two groups in the larval 
state, which in fact goes so far, that Brauer* has no hesita- 
tion about arranging the larva of the flea in his group of 
orthoraphal eucephalous Dipterous larva3. In opposition to 
* Brauei', "Km-ze Charakteristik der Diptereularven," in Verb, k.-k, 
zool.-bot. Ges. in VVien, 18G9, p. 846. 
Dr. Karl Kiapelin on the Pulicidss. 43 
this, however, we must not forget that maggot-like larvae also 
occur in groups far removed from the Flj-type, in Hymeno- 
ptera and Beetles, and therefore cannot possibly be of decisive 
importance in judging of relations of affinity ; as also, on 
tlie other hand, that the pupa of the Fleas witli its quite 
separate Hmbs differs so much at least from the general 
type of the mummy-pupre, that from this very fact it has 
been attempted to set up a relationship of the Fleas to the 
Hymenoptera *. Hence the point of the question how far 
the analogous characters in Diptera and Pulicidgs depend 
upon true phylogenetic affinity would have to be sought 
in the investigation whether the construction of the sucking- 
apparatus is carried out in both cases on the same plan, 
i. e. with the same employment of homologous parts. That 
it is only from this discussion and from that as to the 
structure of the thorax and its appendages that a real decision 
of the question before us can be arrived at, may indeed be 
deduced from the consideration that in these organs we find 
the only characters which, on the one hand, are confined to 
the order Diptera, and, on the other, may be traced tlirougli- 
out their whole series of forms, and therefore must be regarded 
jcar' e^ox')*' ^S typical. 
The structure of the buccal apparatus of the Pulicidas has 
been very frequently discussed without the question of its 
relationship to the sucking-apparatus of other groups of 
insects having as yet been solved. Thus to cite only a 
few : — Dug^s f thinks that the proboscis of the fiea may be 
placed side by side with that of the Tabanidas, but also finds 
resemblances to the Hippoboscidae and Apidre. L. Landois| 
suggests a resemblance of the mouth-apparatus of the Puli- 
cidai to the rostrum of the Hemiptera ; while Taschenberg§, 
again, thinks he recognizes the Dipterous type, and espe- 
cially calls attention to the presence of a " tongue " as 
the most characteristic part of the moutli of a fiy. This ex- 
traordinary diversity of opinions is principally to be ascribed 
to the uncertainty of the interpretation of this very " tongue " 
of Taschenberg's. The mandibles, maxillas, and labium 
have long since been recognized with certainty ; but the un- 
paired piercer " (to express myself neutrally) has been referred 
to as the labrum (Westwood, HaJler, Bonnet), as the hypo- 
* As by Duges, hi his " Reclierches sur les characteres zoolog-iques 
du genre Pulex," in Ann. Sci. Nat. tome xxvii. p. 157. 
t Loc. cit, p. 151. 
i L. Landois, ''Anatomie des Ilimdeflolies," in JSTova Acta Acad. 
Leop.-Car. 1866, p. 56. 
§ Loc, cit, p. ■11. 
44 Dr. Karl Krapelin on the Pulicidge. 
pharjnx (Gerstfeldt), as the epipliarjnx (Karsten), and lastly, 
as already mentioned, as the '' tongue" (Savigny, Taschen- 
berg), and therefore all serious homologizing must have been 
prevented, the more, as even the real components of the suck- 
ing-tube were not made out with certainty. 
In figs. 10 and 13 I give two transverse sections through 
the anterior part of the Pulicid proboscis. Fig. 10 represents 
a section from Palex irntans ; fig. 13 a simihir section, but 
nearer the base of the proboscis, from Sarcopsylla penetrans'^ . 
The sections show at once that the structure of the sucking- 
tube in tlie two most distant groups of the Pulicidse is quite 
accordant. In both cases it is the mandibles hnd), which, in 
conjunction with the " unpaired piercer," form tlie true food- 
canal ; embracing the latter above and laterally, they join 
firmly together in the median line below. A glance of com- 
parison at figs. 1-3 shows that this " unpaired piercer " is 
hollowed into a groove on the underside exactly in the same 
way as the lahrum of the Diptera, and that to begin with 
there is no hypopharynx, but at the utmost perhaps an 
epipharynx. But if we trace the further course of this struc- 
ture by the aid of longitudinal and transverse sections it is 
easily seen that its upper covering immediately after its en- 
trance into the capsule of the head is in chitinous union with 
the upper margin of the arch of the head, while the inferior 
plate, i. e. the one which immediately forms half the sucking- 
channel, passes continuously into the chitinous covering-wall 
of the pharynx. Consequently we find in the organ in ques- 
tion precisely the same conditions as in the labrum of the 
Diptera, and there is no doubt at all that we have to do here 
with a true labrum. A connexion of this with the labium 
by means of a strongly chitinized, brown uniting piece, as 
asserted by Duges (/. c. p. 150), really has no existence at allf, 
and this removes the last possibility of regarding this struc- 
ture as a " tongue," i. e. as an extension or appendage of the 
labium. 
The interpretation of the " unpaired piercer," as labrum, 
being thus established beyond a doubt, the comparison of the 
proboscis of the flea with that of the Diptera can present no 
further difficulties. The employment of the labrum {Ir) as the 
unpaired covering lamella of the food-canal is apparently the 
same in both groups. But it is otherwise with the other 
components of the sucking-tube. In place of the horizontally- 
* The material was kindly sent to me from Assumption by my honoured 
colleague Dr. H. Toppen. 
t This chitinous piece rather forms the lever for moving the mandible, 
a.s will be shown elsewhere. 
Dr. Karl Krapelin on the Pulicidse. 45 
placed mandibles of the Tabanidte and Culicidce, which, as is 
proved by those Diptera which do not pierce, are only secon- 
darily implicated in the closure of the sucking-canal, we see 
in the PulicidjB the vertically- placed mandibles, bent in 
towards each other laterally, appear as integral parts of that 
tube — a different inferior closure, such as exists in the hypo- 
pharynx throughout the whole group of the Diptera, being 
here entirely deficient. This absence of the hypopharynx, 
which, as is clear from what has been said, has as its conse- 
quence a totally different importance of the mandibles, and 
consequently a perfectly peculiar type of sucking-tube"^, 
proves in like manner of importance as regards the discharge 
of the salivary glands. The unpaired salivary duct in the 
lumen of the hypopharynx is replaced in the Pulicidaa by 
paired extremely fine half-tubes (fig. 13, s), each of which, 
running along the inner side of a mandible, may be traced 
from the basal part of the latter as a closed duct into the 
interior of the head, and, further, as far as the thoracic 
salivary gland !• 
Equally great differences in their arrangement and physio- 
logical importance may be demonstrated by a comparison of 
the other constituents of the proboscis of the flea with the 
homologous organs of the Diptera. A labium unpaired 
throughout its whole length, and at the utmost furnished at 
its apex with one-jointed terminal lobes, occurs nowhere 
among the Pulicidse, although something of the kind was 
formerly ascribed to Sarcoj^sijUa. The labium of Sarcojys^Ila 
at least presents (as fig. 8 may show) a biarticulation of the 
" palpi," even with an indication of further segmentation, so 
that in this point also the unity of the Pulicide group appears. 
This difference of the segmentation of the labium in Diptera 
and Fleas, with which a typical difference in the relative length 
of the unpaired basal part to the paired section to be regarded 
as palpi, goes hand in hand, can, however, hardly be so highly 
estimated in its phylogenetic significance as the further fact 
that the labium of the Diptera shows quite a different attach- 
ment to the head, and so has quite a different physiological 
value from that of the Pulicidse. In the former it generally 
attaches itself by its gradually widening base to a more or 
* Particular attention may here be directed to the two peculiar lateral 
lamellae of the labium, which apparent!}', by their elasticity, force the 
upper parts of the mandibles asunder, and thus bring about a closer appo- 
sition of their lower parts. 
t Kraft and Landois believe that they have demonstrated an opening 
of the thoracic salivary glands into the oesophagus not far from the region 
of the neck (see Landois, I, c. p. 18). 
46 Dr. Karl Krapelin on the PulicidEe. 
less developed cephalic cone, with the upper lateral parts of 
which it is connected, and so is enabled from the base onwards 
to form that sheath of the delicate piercing apparatus (the 
two pairs of jaws as well as the labrum) which often arches 
together above so as to constitute almost a closed canal. In 
the Fleas, on the contrary, there is no such union of the 
labium with the lateral or upper parts of the head ; it simply 
articulates with a firm brown chitinous piece (fig. 9, cJi) 
in the median line of the lower surface of the head, and this 
union, as is well known, is frequently so loose that it is 
difficult to obtain Sarcopsyllce^ for example, with the labium 
preserved *. Hence, in its basal part, it does not form the 
sheath for the piercing-apparatus, but shows only a compara- 
tively shallow groove (fig. 15), which only in the ante- 
rior section of the proboscis, when the stem of the labium has 
become cleft into the paired palpi, becomes developed, at least 
in Pulcoc^ into two flaps, embracing the piercing-organ at the 
sides (fig. 10, Ip). But to make up for the deficient protec- 
tion of the basal part of the sucking-tube (and in this we have 
a fundamental deviation from the type of the Diptera) the 
maxillaj hava come in, originating as two broad plates from 
the whole length of the side of the head, and taking here, not 
only the constituents of the piercing-apparatus, but also the 
base of the labium, under their protection, as shown by fig. 15 
in Pulex. 
We seek in vain for analogies to all these characters among 
the Diptera, and we may therefore be justified in asserting 
that all the parts of the Pulicide proboscis (with the sole 
exception perhaps of the labrum) differ so much in position 
and employment from the homologous parts in the Diptera, 
that we cannot well speak of direct phylogenetic relations 
between the two types of proboscis. 
We arrive at precisely similar conclusions as to the rela- 
tionship of the Pulicidaj and Diptera when we take into 
consideration the second group of characters peculiar to the 
Diptera, Avhich appear in tlie structure of the thorax and its 
dorsal ojypendages. Instead of the always freely movable 
head of the Diptera, we find a broad union of it with the pro- 
thorax in the Pulicida3 j instead of the compact thorax with 
its scutellum, Avhich is so characteristic even of the wingless 
Pupipara, we have three sharply separated thoracic segments, 
without a trace of any such dorsal mesothoracic process ; and 
instead of the pair of wings and the halteres, the latter of 
which are aborted only in the most extreme cases of parasitism, 
* Even in recent handbooks we may find the statement that the 
labium of Sarcopsylla is indistinct. 
Dr. Karl Krapelin on the Pulicldae. 47 
there is nothing, absolutely nothing, that could lead us to 
conclude that the Fleas were formerly in possession of any 
such organs. Even tlie marked tripartite condition of the 
thorax ought a priori to have banished the idea of rudi- 
mentary wings ; nevertheless the older authors (Kirby, Dug^s, 
&c.) have fallen into the serious error of regarding separated 
lateral margins of the thoracic segments as such. But these 
*' processes of the pleura3," as Taschenberg * among others 
has conclusively proved, have nothing at all to do with wing- 
rudiments, and are to be regarded as characteristic structures 
sui generis. When Taschenberg therefore for this reason 
declares the generally-employed denomination of '' Aphani- 
ptera," founded upon this erroneous conception, to be inad- 
missible, we can only agree with him. It is only by giving 
up this name that we can seriously hope that the deeply 
rooted notion of the " Diptbres sans ailes," as Strauss-Durck- 
heim called the Fleas, will be completely suppressed. 
The wide gap which exists precisely in the most important 
characters between the Pulicida3 and the Diptera must have 
been made sufficiently evident by the preceding remarks. 
That it is also expressed in other systems of organs than those 
hitherto considered may therefore only be briefly indicated. 
The sucking- stomach, which apparently is met with in all 
groups of Diptera, is entirely wanting in the Pulicidfe j 
while, on the other hand, the proventriculus beset with nume- 
rous chitinous spines of the latter has no analogy among the 
Diptera. The sucking-mechanism of the pharynx or of the 
so-called " fulcrum " of the Diptera is formed by a single 
powerful pair of muscles 5 in the Fleas, on the contrary (as 
in the Rhynchota), a whole series of separate pairs of muscles 
(which, however, are interpreted by Landois as flexors and 
retractors of the labrum) are present for this function. Lastly, 
the presence of a stigma in the prothorax of the Fleas indi- 
cates more profound differences in the tracheal system 5 while 
as regards the simple ocelli of the Pulicidai and the deep 
lateral pits of the head, we may find analogous phenomena 
among the Rhynchota, but not among the Diptera. 
After all this the Fleas cannot well remain in the order 
Diptera. There remains then the investigation of the ques- 
tion whether they show near relations to any of the other 
groups of insects. Hymenoptera and Orthoptera, of which 
earlier authors have thought in this connexion, cannot well 
come into the question in the present state of our knowledge, 
as it would be opposed to all rational system to assert a reia- 
* Loc. cit, p. 21. 
48 Dr. Karl Kriipelin on the PulicidEe. 
tionship of the Fleas to the Hymenoptera upon the sole 
accordance of the pupse, or to the Orthoptera upon the 
segmentation of the thorax. The order Lepidoptera also 
cannot agree in a single one of the more important characters 
with the Pulicidas, and thus there remains only the group 
Ehynchota for serious comparison. As a matter of course, 
considering the fundamental difference of development between 
Pulicidje and Rhynchota, we can hardly expect to find real 
intimate relations between the two groups, at least not so 
close as we must postulate for forms of one and the same 
order ; nevertheless 1 think I may indicate some points of 
view which deserve to be well considered in judging of the 
phylogenetic connexion between Fleas and Rhynchota. 
In the first place there can be no doubt that the order 
Rhyncliota does not even ap])roximately present a unitary 
type in the same degree as that of the Diptera. We find 
united in it animals with suctorial and masticating buccal 
apparatus, with perfect, imperfect, and without metamorphosis. 
The head is sometimes freely movable, sometimes attached by 
a broad surface to the prothorax. The thorax, so very uni- 
formly constructed in the Diptera, shows all possible stages 
of structure, from the enormous development of the sepa- 
rated prothorax in Scutata and Membracina, to the compact 
thorax sliowing scarcely an indication of segmentation of the 
Pediculina, or tliat of many Mallophaga more or less sharply 
divided into three distinct segments ; and like the thorax 
itself, its dorsal appendages also present no unity of type. 
With such polymorphism of almost all organs it is easily intel- 
ligible that we should be able to find in this Protean group ana- 
logies for a whole series of characters of the Pulicida\ Thus the 
segmentation and winglessness of the thorax in the Fleas may 
be without difficulty placed side by side with the similar con- 
ditions among the Mallophaga, which, at the same time, 
present examples of the antcnnary pits of the head already 
mentioned. The absence of facetted eyes in Pulicidffi agrees 
with what occurs in Coccida^, Pediculina?, and Mallophaga, 
the pupa enclosed in a cocoon unites them with the Coccida? ; 
the absence of sucking-stomach and the number of the 
Malpighian vessels and testes are even common to them and 
to all forms of Rhynchota. 
For the reasons above given, however, we must not ascribe 
a serious significance to all these agreements unless the 
Rhynchotan type sought for finds expression at least in the 
last of the cliaracters to be discussed, those of the buccal 
apparatus, and shows near relations to the homologous organs 
of the Fleas. According to the present state of our know- 
Dr. Karl Krapelin on the Pulicidae. 49 
ledge it cannot well be maintained that there is a clear imi- 
tariness of structure in the buccal organs of the Rhynchota, 
as, at any rate among the Aptera (the Pediculina and Mallo- 
phaga), conditions occur which depart widely from those of tlie 
more highly organized groups. But as the arguments upon 
this point are not yet closed and I have made no investigations 
upon these lower forms, we must content ourselves with 
examining at least the sucking-apparatus of the Hemiptera 
and Cicadae in search of any agreement with the proboscis 
of the Fleas that may exist. With regard to the arrangement 
of the parts of the mouth in these higher groups of the Rhyn- 
chota, I have already published some statements in a previous 
note *, and these observations have since been confirmed and 
extended by Geise f- According to these the true sucking- 
tube of the proboscis is formed by the two maxillee closing 
laterally against each other into a double tube, while the 
mandibles are placed alongside of this tube as lateral piercing- 
setfe. From more recent investigations I do not hesitate to 
declare this view J so far erroneous that it is not the maxillne 
but rather the mandibles that interlock in the median line to 
form the sucking-tube (see figs. 11, 14). I am led to this 
changed interpretation of the two pairs of jaws in the first 
place by the fact that in transverse sections through the head 
the lateral setse finally come to be the lower ones, as, indeed, 
Geise correctly shows in his figs. 25 and 31. Secondly, I 
think that in the Cicadae I have found distinct traces of basal 
joints of the maxillae connected with the outer setffi. Fig. 12 
shows the lower part of the face of a large tropical Cicada. 
On each side of the broad labrum (Ir) there is here an oblong 
plate ipl), which terminates almost in the middle line 
beneath the labrum in a blunt hairy tubercle and a peculiar 
whip-like appendage (fig. 6,/) . If this structure be prepared 
out of the head, a connexion, certainly only by articulation, 
with the lateral piercing sette may be easily demonstrated, 
for protrusion and retraction of which not only the chitinous 
sinews (fig. 6, sp and sr), but also the corresponding muscles 
(tig. 6, pm and rm) are attached to this chitinous piece. If 
this interpretation of the chitinous piece occurring in all 
Cicada3, I ulgorinse, &c., as the basal part of a jaw, perhaps 
even with palpiform appendages, be correct, this must, of 
* Zool. Anzeiger, 1882, p. 574. 
t G-eise, ' Die Mundtheile der Illiynchoten ' (Bonu, 1883). 
X On my part this resulted merely from what I now believe to be a 
wholly unjustified homologiziiig with the buccal organs of the Lepido- 
ptera, the sucking-tube of which is undoubtedly formed of the maxilla 
(see also Kirbach, Zool. Anz. 1883, p. 553). 
Ann. iic Mag. N. Hist. Ser. 5. Vol. xiv. 4 
50 Dr. Karl Krapelin on the Pulicidse. 
course, be a maxilla, and thus the composition of the sucking 
tube out of the two mandibles would be finally decided. Bu 
then we should at once be enabled, in one point, to carry ou 
a corresponding comparison between the buccal organs of the 
Pulicida3 and Rhynchota, inasmuch as we need only suppose 
the labrum of the latter, which is indeed often enough developed 
into along, slender, stylet-like organ, to sink from above be- 
tween the mandibles*, in order to arrive at conditions which 
might perfectly well be placed side by side with those occur- 
ring in Pulicidse (compare fig. 11 with fig. 15). It appears 
further that upon the basis of my conception a connexion 
might be established between the modes of discharge of the 
saliva in the Pulicidge and Rhynchota, if we assume that the 
paired half-grooves along the inner side of the mandibles of 
the Pulicidge (fig. 13, s) have coalesced in consequence of the 
changed adhesion of these jaws, caused by the emergence 
of the labrum, as a constituent of the sucking-tube, into an 
unpaired efferent canal (figs. 11 and 14, s). The variable 
part taken by the two mandibles in Hemiptera and Cicadge 
(see fig. 14) in the formation of this salivary tube would 
come in support of this hypothesis. Among the lihyn- 
chota, as is well known, a hypopharynx is not developed as a 
separate organ, or only as a rudiment (in Cicadaj), so that in 
this circumstance also a parallelism between Pulicidge and 
Bugs may be found. 
The labium of the Rhynchota consists of four consecutive 
cylindrical joints furnished with a deep longitudinal groove 
along the upper surface. It has been said that it is destitute of 
pgilpi, but I think that this mode of expression is not correct. A 
labium divided into four or five successive rings is in complete 
contradiction to the plan of the organ deduced from the con- 
sideration of the masticating mouth. But notwithstanding 
Geise's assertion to the contrary {I. c. p. 11), there is nothing 
to prevent our regarding the cylindrical and often much more 
voluminous basal part of the labium as the submentura 
and raentum, as a direct continuation of which arise the 
multiarticulate palpi fused together in the median line. 
That there is really an amalgamation in the terminal 
joint of the labium is rendered probable by the circum- 
stance that both in the Hemiptera and in Cicadge a pretty 
* Geise asserts sometliing of the kind when he represents the labrum 
in C'oriva and Sigara as taking part with the constituents of the sucking- 
tuhe {I. c. p. 53, fig. 29) ; unf(jrtunately I must reject this assertion — 
welcome as it would be to me tor the homology attempted above — as 
positively erroneous. 
Dr. Karl Krapelin on the Pulicidse. 51 
considerable notch appears at the apex*, although the side 
lobes thus produced are not jointed off from tlie unpaired piece 
in the same way as is usually the case, with the labella of the 
Diptera for example. But if this conception of the structure 
of the labium of the Rhynchota be correct, a comparison of it 
with that of the Pulicidse presents no difficulties. A fusion 
of the longitudinal fissure of the labium of Sarcopsylla (fig. 8), 
for example^ nearly to the apex, would essentially realize for 
us the conditions existing in Rhynchota (compare the labium 
of Cicada in fig. 5). And with this apparent equivalence of 
the parts an approximately similar physiological application 
of them would be associated. 
It has already been pointed out that the labium of the 
Pulicidie has undertaken the guidance of the sucking-tube 
only in its distal and not in its proximal part. But exactly 
the same thing may be asserted of the labium of the E,hyn- 
chota, which in the basal section of the rostrum shows an 
effacement of the dorsal furrow and decidedly turns down- 
wards, and thus devolves the guidance of the sucking-canal 
and of the piercing setge entirely upon the labrum. In the 
latter circumstance, indeed, there is an essential difference 
between the proboscis of the Fleas and that of the Rhyn- 
chota, as in the former the labrum, which has become one 
of the constituents of the sucking-tube, cannot possibly be 
employed to envelop the whole apparatus. But precisely 
this different application of the labrum renders intelligible 
a further fundamental difference between the two types of 
proboscis, which must be found in the physiological appli- 
cation of the maxilla3. In the sucking-tube of the Rhyn- 
chota, which^ under the double guidance of the labium and 
labrum, is sufficiently enveloped and protected throughout its 
whole length, the maxillte might, without damage, be brought 
in to complete the true piercing-apparatus ; they have become 
long thin structures, destitute of palpi. Hanking the sucking- 
tube. In the Pulicidse, on the contrary, in which the basal 
section of the sucking-tube, in consequence of the peculiar 
employment of the labrum, was destitute of an envelope, 
the maxillai^ developed into broad plates (figs. 4 and 7 and 
\b^m)^ had this important function of protection transferred 
to them. That under such a change of function the palpi 
* The section across the tip of the rostrum of Notonecta (fig. 14) shows 
the labium as consisting of two perfectly separate parts. Geise's state- 
ment that in Corn a the third and fourth joints of the labium are com- 
pletely cleft, depends, according to my investigations, upon an erroneous 
interpretation of the conditions coming into view at the tip of the 
rostrum. 
4* 
52 Dr. Karl Krapelin on the Pulicidge. 
also came to full development and importance, can hardly 
be regarded as a serious obstacle to the homology here 
attempted. 
The preceding indications will suffice to prove that in fact, 
without any great violence to the data given, a certain parallel 
may be drawn between the buccal organs of the Fleas and 
those of the higher Rhynchota, and that this comparison is at 
least far easier to carry out than that between the Pulicidge 
and the Diptera. If we bring the other agreements and diffe- 
rences of the three groups in question into the account, the 
result must be a phylogenetic alliance, although a distant one, 
of the Fleas with the Rhynchota rather than with the Diptera. 
But I repeat that the demonstrated relations certainly by no 
means justify a union of the two groups. The only possi- 
bility that presents itself is therefore to place the Pulicidse as 
an equivalent order Siphonaptera "^ side by side with the two 
most nearly allied orders. 
The entire series of insects with suctorial mouth-organs 
would consequently have to be divided in the first place into 
two groups, one of which (Hymenoptera, Lepidoptera) is 
characterized by having the lower parts of the mouth, maxillse, 
and labium employed in the formation of a sucking-apparatus, 
while in the other, on the contrary, it is almost exclusively 
the upper parts (labrum and mandibles) that are implicated 
in the formation of the true food-canal. This latter group 
would include the three orders Diptera, Siphonaptera, and 
Rhynchota, which 1 may, in conclusion, briefly characterize 
as follows : — 
1. Diptera. Insects with perfect metamorphosis. Head 
free, with facetted eyes. Sucking-tube formed by a dorsal 
and a venti'al half-channel (labrum and hypopharynx), more 
or less enclosed throughout its length by the labium, which is 
bent up like a sheath and furnished with uniarticulate apical 
palpi. Mandibles deficient or styletiform, pushing in between 
the labrum and hypopharynx. Maxillge, when present, with 
palpi. Salivary efferent duct an unpaired closed canal in the 
interior of the hypopharynx. A " sucking-stomach." Tho- 
racic segments amalgamated, usually with a pair of wings and 
a pair of halteres. 
2. Siphonaptera. Insects with perfect metamorphosis. 
Head attached to the thorax by a wide surface, without 
facetted eyes. Buccal organs suctorial. Sucking-tube formed 
* As the name " Aphaniptera " is inadmissible for reasons already 
given, and that adopted by Taschenberg-, " Suctoria," has already been 
employed twice, for a group of Oirripedes and for the Acinetse, I think 
it best to fall back upon Latreille's name " Siphonaptera." 
Dr. Karl Krapelin on the Pulicidge. 53 
by a dorsal and two lateral channels (labrum and mandibles) . 
its anterior section only more or less enclosed laterally by the 
multiarticulate terminal palpi of the labium, and at the base, 
besides the latter, by the lamelliform palpigerous raaxillge. 
Salivary efferent ducts paired, developed as a channel along 
the inner surface of the mandibles. No "sucking-stomach." 
Thoracic segments free, without wings and halteres, with 
pleural processes upon the last two segments. 
3. Rhynchota. Insects usually with imperfect metamor- 
phosis. Head free or broadly united to the thorax, with or 
without facetted eyes. Buccal organs usually suctorial. 
Sucking-tube (in the higher groups) composed off two lateral 
half-channels (the mandibles), only in the anterior portion 
enclosed by the labium and its apical multiarticulate palpi, 
which are united nearly to the apex ; at the base by the 
labrum. Maxilla styliform, without palpi, applied laterallv 
to the mandibles in the channel of the labium or the labrum. 
Salivary efferent duct unpaired, formed by two half-channels 
of the mandibles closing too-^^ther from the sides. No 
" sucking-stomach." Thoracic segments free or amalga- 
mated. Four, two, or no wings ; no halteres. 
EXPLANATION OF PLATE UI. 
The letters in all the figures refer to the same parts: — Ir, labrum; 
m d, mandibles ; m, maxillae ; m t, maxillary palpi ; /, labium ; I p, labial 
palpi ; /*, hypopharynx ; n, food-canal ; s, salivary duct. 
Fiy. 1. Transverse section through the proboscis of Tabanus, sp., anterior 
third. 
Fiff. 2. Transverse section through the proboscis of Melophaffus ooinus, 
middle. 
Fiy. 3. Transverse section through the proboscis of Culex pipiens $> 
middle. 
Fi(j. 4. Maxilla of Sarcopsylla penetrans, side view. 
Fiy. 5. Labium of Cicada, sp., side view. 
Fig. 6. Lower part of the maxilla of Cicada sp., and its union with a 
lamelliform appendage {pi) of the fore part of the head. /', 
whip-like process of the plate ; p m, protrusor ; /■ m, retractor of 
the maxilla ; sp and s r, the sinews belonging to them. At .v the 
sinew of the protrusor articulates with a chitinous rod which is 
perpendicular to the surface of the plate, and therefore does not 
appear distinctly in the figure. 
Fiy. 7. Maxilla of Pidex irritans. 
Fiy. 8. Labium of Sarcopsylla j^enetrans from above. 
Fiy. 9. Tjabium of Ptdex irritans, side view, ch, basal chitinous piece. 
Fiy. 10. Transverse section through the proboscis of Ptdex irritans, an- 
terior third. 
Fiy. 11. Transverse section through the rostrum of Notonecta ylauca, 
basal third. 
54 Dr. O. Zacharias on the Development 
Fig. 12. Front view of tlie head of Cicada sp. i^l, plates with which 
the maxillae articulate. 
Fuj. 13. Transverse section through the proboscis oi Sarcopsylla penetrans, 
middle. 
Fig. 14. Transverse section through the rostrum of Notonecta glauca, 
apex. 
Fig. 15. Transverse section through the proboscis of Pulex irritans, base. 
VI. — New Investigations on the Development of the Viviparous 
Aphides. Bj Dr. Otto Zacharias *. 
Since the appearance of Metschnikoff's ' Embryologische 
Studien an Insecten ' (1866) the development of the embryo 
of the viviparous Aphides has not again been made the sub- 
ject of a monographic investigation. What the Russian 
author established with regard to the mode of development of 
the "pseudova" of Aphis Rosce and A. Pelargonii -passes pretty 
generally for all that is observable at present. Metschnikoff's 
description of the development of Aphides (at least in its 
fundamental features) is regarded as a " rocher de bronze," 
which presents no point of attack for an incisive criticism. 
This, however, is not the case, and I will, in a memoir that 
will appear very shortly, furnish the proof that Metschnikoff's 
description of the Jirst developmental stages (as far as the 
formation of the S-shaped germinal streak, and even some- 
what later) by no means agrees with the facts. For the 
subsequent stages I have also obtained quite different results 
of investigation, which I shall venture to summarize at the 
conclusion of this preliminary note. 
The observation of the embryonic development of the vivi- 
parous Aphides is for many reasons a difficult matter. 
Besides the minuteness and delicacy of the objects with which 
we have to do, there is a third condition which causes many 
obstacles to the investigation, namely the clearness and strong- 
refractive power of the protoplasmic contents of the egg. If 
in the case of the eggs of many other insects we have to 
contend with the obscurity of their yelk, it is in the Aphides 
the crystal clearness of the latter which frequently acts very 
prejudicially : prejudicially, inasmuch as under the circum- 
stances indicated the upper half of the egg constantly acts 
upon the lower half (or vice versa) ^ like a lens with a very 
short focus, and not only enlarges but also distorts those 
* Translated from the ' Zoologischer Anzeiger,' no. 168, May 26, 1884, 
pp. 292-296.