112 M. Blanchard on the Circulation in Insects. 
(Hyalonema) ; and in some instances, from a mixture of membra- 
nous tissue with the earthy matter, they resemble cork. 
4. Among the calcareous corals the texture or density of the 
coral is often of little importance, as it may vary in different parts 
of the same specimen, according to their full exposure to the free 
ocean waters or not. 
In species with stellate cells there is always a definite number 
of rays to the adult cell, excepting among those that bud in the 
discs, and this number is some multiple of four or six, and usually 
of both. The characters of the cells — whether immersed or occu- 
pying a prominent calicle; and, internally, deep and open at 
bottom, or transversely septate, or spongy cellular or solid, — are 
important ; also the peculiarities of the lamellae, whether entire 
or not, equal or irregular, exsert or included. 
In transverse sections of the stellate cells, the number of rays 
(when adult), the diameter, and the character of the centre and 
of the interstices, are generally good characteristics for species. 
The corals of Alcyonaria never have rays to their cells or tubes ; 
the Madreporacea have never more than twelve rays ; the Caryo- 
phyllacea and Astrseacea have always more than twelve ; and the 
last order is distinguished by having the interval between the 
cells lamello-striate (see p. 109, III. 2) internally, with few ex- 
ceptions, as well as externally. 
This brief review of the characteristics of zoophytes has pre- 
pared the way for an exposition of the classification into which 
the species naturally fall. 
[To be continued.] 
XIII. — On the Circulation in Insects. By Emile Blanchard*. 
The celebrated author of the ( Anatomie Comparee/ finding no 
other vessels in insects than the dorsal one, believed that no true 
circulation existed in these articulated animals. According to 
Cuvier, the trachese ramifying throughout the entire body of the 
animal, the air in them must proceed in search of the blood, just 
as, in animals having a pulmonary or bronchial respiration, the 
blood is conveyed to the air. 
Since his time, many anatomists have studied the circulation 
in insects. They have usually selected transparent larvse which 
have allowed them to distinguish, through the tegumentary en- 
velope by the aid of the microscope, currents of liquid blood. In 
this manner Carus observed a circulatory movement in the larvae 
of the Ephemeridse and Agrions. Wagner, Bowerbank, Newport, 
and others have verified these facts. According to these observers, 
- . * Translated from the Comptes Rendus for May 17, 1817. 
M. Blanchard on the Circulation in Insects. 113 
the entire circulation in insects is reduced to this : the blood, 
urged forwards by the dorsal vessel, bathes the organs by being 
poured into the cavities of the body, where a retrograde move- 
ment causes it to return into the dorsal vessel by orifices at its pos- 
terior .part. Leon Dufour, who has contributed so much to our 
knowledge of the organization of insects, denies, with Cuvier, the 
existence of any circulation whatever in these animals. According 
to that anatomist, the dorsal vessel is only a simple cord, without 
an internal cavity. Its movement, he says, is only the result of 
the simple contractility of its tissue, a kind of fibrillar vibration 
common to many living tissues. 
Such are the various opinions regarding the circulation in in- 
sects. What might perhaps have caused surprise, was that, in 
accordance with the ordinary explanation, the circulatory and 
respiratory apparatus were to a certain extent independent, the 
tracheae, according to the general opinion, not coming into con- 
tact with the nutritive liquid except by currents traversing the 
lacunae between the organs. However, this did not attract atten- 
tion. Their study by the aid of their transparency, not allowing 
of accurate details being distinguished, the question has always 
remained much in the same state. 
A very simple means, however, of tracing the whole course of 
the circulation in insects would have been to inject coloured 
liquids, llecourse has not been had to this proceeding ; or if so, 
no benefit has been derived from it. Nevertheless, among the 
invertebrate animals, there are few in which this means of inves- 
tigation so easily yields a good result. Whether we inject by the 
dorsal vessel or the lacunas, the entire circulatory system is im- 
mediately filled. Nothing is more remarkable and elegant than 
an insect properly injected : all the tracheae, which ramify 
throughout the organs in such delicate branches, are coloured by 
the injection; however, not even the smallest drop of liquid 
penetrates their interior. 
The tracheae of insects, as well known, are composed of two 
membranes between which there is a thread spirally coiled. The 
sanguineous fluid penetrates between the two membranes. Every 
part of it thus comes into contact with the air contained in the 
tracheal tubes, and the re-organization of the blood is effected as 
in animals furnished with lungs, although the anatomical dispo- 
sition is so different. This observation explains the structure of 
the tracheae. The spiral thread not only serves to give them a 
certain solidity, it has also the purpose of keeping the two sheaths 
of which they are composed apart, and of keeping them open 
near the respiratory orifices so as to give passage to the nutritive 
fluid. When the tracheae are vesicular the spiral thread disap- 
pears, and then the very numerous and excessively fine canals 
114 M. Blanchard on the Circulation in Insects. 
traverse them in all directions. If we inject an insect by the 
dorsal vessel, the liquid, after having traversed it in its whole 
extent, is soon poured into the lacunae of the head and thorax, 
and is diffused into the abdominal lacunae. It then penetrates 
between the two tracheal membranes by lacunae which surround 
the respiratory orifices ; finally it is returned to the dorsal vessel 
by lateral afferent canals, which extend over the dorsal parts as 
far as the origin of the tracheal bundles. Thus these afferent 
canals are equal in number to the stigmata of the abdomen ; it is 
the same with the number of segments of the dorsal vessel, which 
also varies according to the types. 
The tracheal tubes, therefore, which convey the air into all 
parts of the body also carry the re-oxygenated blood to all the 
organs : the space existing between the two sheaths of the respi- 
ratory organs appears to perform the office of nutritive vessels. 
The circulation in insects is effected therefore in the same man- 
ner as in many invertebrate animals which have a partly lacunar 
circulation. But there is a very peculiar anatomical disposition : 
the activity of the circulatory movement here as elsewhere is in 
relation with the activity of the respiration. 
I have investigated the circulation in a tolerably large number 
of genera of insects, so as to be assured that there is no essential 
difference between the different types of the entire group. I am 
convinced that the anatomical modifications are very trifling, even 
between the representatives of the different orders of this large 
class of animals. 
My observations have been made, in the order Coleoptera, 
principally upon species of Melo'e, Dytiscus, Hydrophilus, Geo- 
trupes, &c. ; in the Orthoptera, especially upon Blatta ; in the 
Hymenoptera, upon the Humble Bees, Wasps, and especially on 
the Bee ; in the Hemiptera, upon Nepa and Ranatra ; several on 
Lepidoptera and different Caterpillars, and on some Diptera both 
in the larval and perfect state. 
Throughout I observed the same facts, and I have proved that 
the larvae and the adult insects do not differ in any but unim- 
portant relations. 
The facts I have detailed may very soon be verified by merely 
injecting a coloured liquid through a simple aperture in the 
abdomen of an insect : in this way all the lacunae are immediately 
filled, as also the vascular portion of the tracheae, and ultimately 
the dorsal vessel itself.