102 Miscellaneous. On the Organization of the Acarina of tlie Famihj Gamasidae — Cha-racters which prove that they constitute a natural Transition between the Hexapod Insects and the Arachnida. ByM. M^gni^st. In our opinion the type of the family Gamasidae is the genus Uropoda and not Gainasus *, because it is the Uropodce that present the most perfect organization, most nearly approaching that of insects and even of the highest insects. This goes so far that we might perfectly well maintain that they are true Hexapoda, seeing that the feet of the first pair form an integral part of the organs of the mouth, and constitute true labial palpi by the union of the coxae of this pair with the mentum, which forms a true labium, and by their insertion within the margins of the buccal cavity. This organization of the UropodcB, so much resembling that of certain suctorial insects, falls off gradually when we pass to the genera Gamasus, Dermanyssus, and Pteroptus, to acquire that which prin-cipally characterizes the Arachnida — that is to say, to become plainly octopod ; thus the ftet of the first pair, which still fulfil the func-tions of palpi, and difier from the rest in the form of the tarsus in the Gamasi and Dermanijssi, in which the coxae are separated from the mentum, become like the rest in form and attachment in the Pteropti, and are then exclusively organs of progression. It is not only by the form and functions of the first pair of feet that the Gamasidae depart from all the other Ai'achnida, but also by the number and form of the parts of the rostrum, the composition of which much resembles that of the Hymenoptera. As in the latter, the maxillae concur to form a tube sheathing the ligula ; this tube is completed superiorly by an advanced labium, which does not exist in the Arachnida; and the complete tube, with the organs it contains, forms a true trunk, shorter than in the Hymenoptera, but movable as in those insects, and containing nearly the same ele-ments. The principal diff'erenee consists in the position and form of the mandibles, which, instead of being short, robust, and attached in front of the trunk as in the Hymenoptera, are in the form of rods terminated by a chela, or of styles sliding in the interior of the rostral tube and moving independently of each other ; they thus remind us in form of the mandibles in the Hemiptera, in some Diptcra, and especially in the fieas. It may be added that we find as accessory parts of the rostrum, besides the large pair of maxillary palpi common to all insects and all Arachnida, a second pair of small cultriform maxillary palpi, of two joints, of which only the terminal one is free and movable, resembling those of the Cicindelidae and Carabidae, or, better still, the gcdea of the Orthoptera — secondary palpi which are not met with in any arachnid of other families. Ihe Gamasidae also possess an independent, movable and setiferous mentum, such as is not presented by any other Acarian family, * See a previous note on this subject, Conipteo lieudus, May .31, 1875.
On the organization of the Acarina of the family Gamasidæ—Characters which prove that they constitute a natural transition between the Hexapod insects and the Arachnida
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