Miscellaneous. 95 



Atax, at each moult, the animal returns to the state of an eg;^, and 

 entirely loses all its old apparent organs. Now it is precisely the 

 same phenomenon that occurs in the Sarcoptidse ; only here the new- 

 egg is formed beneath the old envelope, which is not destroyed as in 

 Atax, no doubt on account of the different medium in which the 

 animals live : in the water the integuments of the male organ of the 

 Atax disappear by dissolving ; in the air the same organs persist, 

 but desiccated. 



When the hexapod larva or the octopod nymph of a Psoroptes, a 

 Tyrogh/pJius, &c. is about to moult, it becomes inert and as if dead; 

 then we see its limbs and rostrum empty themselves, by a sort of 

 liquefaction, of the muscles and other soft parts which they contain. 

 The product of this liquefaction accumulates in the body, becomes 

 granular, surrounds itself with a true blastodermic membrane ; and 

 a true egg is thus constituted within the body of the animal, which 

 it almost entirely fills. 



This secondary egg afterwards presents precisely the same phases 

 as the primary egg which gave birth to the larva, which have been 

 so well described by Claparude : that is to say, its blastodermic 

 membrane becomes mammillated or buds towards the cephalic extre- 

 mity and on the sides. At the former point three pairs of mammillas 

 make their appearance ; two of these give origin to mandibles, two 

 others to palpi, and the last two to maxillae, which quickly become 

 soldered together; a new rostrum is thus formed. The lateral 

 mammillae, of which there are four pairs, become elongated, fold down 

 upon the ventral surface, become cylindrical, then show perfectly 

 marked articulations, and finally become legs with all their acces- 

 sories, such as claws, caruncles, hairs, and spines. When the 

 animal is fuUy formed, it issues from the old envelope, which tears 

 along the dorsal surface and the transverse cephalothoracic furrow, 

 precisely as the larva escapes fi'om the ruptiu-ed shell of the original 

 egg. 



I have traced all these phenomena in two new Tyroglyplii, very 

 common on Agarics attacked by black ' putrefaction ; these I have 

 named Tyroghjphus mycophagus and T. rostroserratus (Megnin). I 

 have also followed them in T. siro (Latr.), in Sarcoptes incurvatus 

 (Megn.), and Psoroptes eqid (Gerv.), in which they are especially 

 easy of observation. 



I have also observed them in several species of Gamasidoe, among 

 others in Pteroptcs vespertUionis (L. Duf.). Here, however, pro- 

 bably in consequence of the enormous volume of the legs, the 

 secondary egg has diverticula which are produced into each of the 

 old ones, and it is in the interior of these Cfeca that the new legs 

 are formed ; thus, at a certain moment, we see the old legs bearing 

 all their accessories, presenting in the interior of their tarsi another 

 foot, with its claws, caruncles, and hairs, the latter laid transversely 

 and longitndinallj' upon the new limb. 



In the Gamasida? the old envelope dcjes not remain entire, as in 

 the Sarcoptida?, but it breaks up irregularly to liberate the new 

 animal which it contains. This explains why we do not find the 



