22-4 A. D. MICHAEL ON THE ACARINA. 



these authors, not feeding upon the juices of, or injurious to, the bird, 

 hut feeding on the feathers only, or keeping them clean. In these 

 Acari the act of coition continues for a long time (as faras has been 

 ascertained probably two or three days), and consequently it is rarely 

 that one examines the feathers of a freshly-killed bird without finding 

 Dermaleichi in copulation. There is a species parasitic upon the jay 

 and other birds, said to have been discovered by M. Robin some con- 

 siderable time ago, why I do not know, as it appears under the same 

 specific name in Kock's work, published long before, which Robin 

 has called " Proctophylodes glandarinus" in which the male organ 

 is of extreme length, and the creature is sufficiently transparent to 

 allow it to be plainly seen through the body — this forms a favour- 

 able subject for observation. The sexual organs in the Dermaleichi 

 are placed in the position above referred to, namely, opening on the 

 sternal surface of the cephalothorax, and usually about centrally 

 between the epimera of the second and third pairs of legs, the male 

 organ being a little further back than the female. The penis is 

 more or less conical, but in some species the cone is short, while in 

 others, like " glandarinus" it is lengthened until it assumes the 

 appearance of a spine rather than a cone. The vulva presents much 

 the same external form as in Glyciphagiis, Tyroglyphus, and many 

 other true Acari, viz., a longitudinal slit with the labia somewhat 

 separated posteriorly, and protected anteriorly by a strong chitinous 

 horse-shoe shaped band called by Robin a sternite, the ends of which 

 are recurved ; this horse-shoe often sends out a straight central pro- 

 jection from its concave side to the anterior termination of the vulva 

 itself, and is frequently supplemented by other smaller chitinous 

 protecting pieces, the entire arrangement forming a very conspicuous 

 feature in the mature female, all signs of external sexual organs 

 being absent in the nymph. It was, however, observed by more 

 than one naturalist, and announced with some hesitation, that what 

 appeared to be copulation took place between the adult male and the 

 female nymph which did not show any external sexual organs, a 

 circumstance not only sufficiently startling in itself but difficult to 

 reconcile with what has been so carefully ascertained by Claparede, 

 and, to a certain extent, by Duges ; the former of whose observa- 

 tions have been lately confirmed by those of Megnin, viz., that the 

 change from nymph to perfect Acaius is not a mere casting of the 

 exo- skeleton, but is an entire dissolution and re-formation of the 

 whole organism, or, as Megnin expresses it, a return to an egg state. 



