102 Miscella n eo us. 



On the Organization of the Acarina of the Family Gamasidae — Cha- 

 racters which prove that they constitute a natural Transition between 

 the Hexapod I?isects and the Arachnida. By M. M^gnin. 



In our opinion the type of the family Gamasidse is the genua 

 Uropoda and not Gamasus *, because it is the Uropoda; 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 Uropodce, so much resembling that of 

 certain suctorial insects, falls off gradually when we pass to the genera 

 Gamasus, Derynanyssus, and Pteroptus, to acquire that which prin- 

 cipally characterizes the Arachnida — that is to say, to become plainly 

 octopod ; thus the feet of the first pair, which still fulfil the func- 

 tions of palpi, and differ from the rest in the form of the tarsus in 

 the Gamasi and JJermanyssi, in which the coxje 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 Gamasidaj 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 Hymenoptcra. As in the 

 latter, the maxillae concur to form a tube sheathing the ligula ; this 

 tube is completed superiorly b_y 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 difference 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 stjdes 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 

 Diptera, and especially in the fleas. 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 

 Carabidfe, or, better still, the galea of the Orthoptera — secondary 

 palpi which are not met with in any arachnid of other families. 



The Gamasidoe 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, Coniples Reudiis, May 31, 1875. 



