Miscellaneous. 75 



There are remarkable diflFerences between the development of the 

 male and of the female. The male undergoes no profound changes 

 in passing from the larval to the adult state. In these two phases 

 of its existence it presents the same peculiarities of structure. Its 

 structure perfectly resembles that which we observe in the Sarcoptidae 

 in general, in which the legs bear long hairs, and some of them, if 

 not all, have also pedunculated suckers. The characteristics of the 

 family which exist in the young persist in the male until the adult 

 state. 



In the females it is otherwise. The changes which take place in 

 the course of development give rise not only to differences which 

 characterize the adult, but also to arrangements which are not met 

 with in other Sarcoptidae. 



At the last moult but one the female appears with its eight legs, 

 its genital aperture, and all its other principal characters. It is then 

 only distinguished from the adult by its not yet having ova in its 

 body, and by the dorsal shield only presenting pointed, conical pro- 

 tuberances, instead of the flattened scales which this region exhibits 

 in the adult. After increasing in bulk it undergoes another moult 

 in order to attain its definitive condition, in which the dorsal surface 

 is covered with flattened scales. These protuberances, which are in 

 themselves of but little importance, are interesting because they also 

 appear in the mites of the genus Sarcoptes, in which they are parti- 

 cularly developed in the female sex. In the species of which the 

 adult females do not present these projections, they are also wanting 

 in the male ; in Sarcoptes scabiei they are found not only in the 

 adult female, but also, although much less developed, in the male. 

 In Dennatoryctes fossor they are exclusively characteristic of the 

 female. M. Ehlcrs thinks that this formation of the skin may have 

 been originally a secondary sexual character of the females which has 

 become a little attenuated in the species under consideration, whilst 

 in other female Sarcoptidae it has maintained itself and even been 

 transmitted to the males by heredity. 



The legs of the females undergo remarkable transformations at the 

 last moult ; they become short stumps which have lost a joint, and 

 no longer possess hairs or suckers. The Sarcoptidae of the Mam- 

 malia present a similar modification, although far less profound ; for 

 the females have their last two pairs of legs destitute of suckers, 

 whilst the males possess them at least on the last pair but one. On 

 the other hand, in Dennatojiharjus and DennatoJcoptes (Fiirst.) the 

 female has a sucker at least in one of the posterior pairs of feet, and 

 in the male we find one on each foot ; this fact is the more remark- 

 able because in these genera the sucker does not exist in the larval 

 state, and only appears at the last change of skin. The two genera 

 in question diff"cr from the true SarcojJtes in not piercing canals in 

 the epidermis of their host, but living more on the surface, concealed 

 by the hairs, the cells detached from the epidermis, &c. The disap- 

 pearance of the suckers and the shortening of the legs consequently 

 seems, in the Sarcoptes, to be in connexion with the mode of life, 

 and especially with the nature of the habitat ; so that those which 



