CHAPTER VI. 



DEVELOPMENT AND IMMATURE STAGES. 



THE life-history of one of the Tyroglyphidae, and of 

 almost all other Acari, may be divided into four prin- 

 cipal stages ; namely, the egg, the larva, the nymph, 

 and the imago. A few exceptional cases occur in the 

 Acarina, where one or more of these stages are practi- 

 cally suppressed, or are passed within the body of the 

 creature when in a different stage. As far as is at 

 present known these cases occur more frequently 

 among the Tarsonemidse than in any other family. 

 Thus in Disparipes bombi and D. exhamulatus the 

 nymphal stage is entirely suppressed, at all events in 

 the male ; although Prof. Canestrini treated the adult 

 male as a hypopial form,* which was an error. The 

 most extreme instance, however, is that of Pediculoides 

 ventricosus, where the whole of the immature stages, if 

 existing at all, are passed within the body of the adult 

 female, the imago being produced viviparously, as was 

 observed by Laboulbene and Megnin ; t I can confirm 

 the fact from personal observation. In the Tyrogly- 

 phidse, however, the nymphal stage is complicated, in 

 some genera, by the curious hypopial stage, which is 

 fully treated of in the latter part of this chapter, and 

 which one would be at first inclined to treat as a 

 separate stage; although that view can scarcely be 

 maintained ; but the hypopial condition is wholly 

 exceptional. 



* ' Can. Pros.,' t. iii (1888), pp. 328, 330. 

 f In ' J. Anut. Physiol.,' t. xxi (1885), p. 16 



