446 THE INVERTEBRATA 



where only two spiracles are retained at the posterior end of the body. 

 The first instar larva of Musca is metapneustic, subsequent instars 

 being amphipneustic (Fig. 326 A). 



Of general interest are the ectoparasitic Diptera, the Hippo- 

 boscidae restricted to birds and cattle, the Nycteribidae and the 

 Streblidae to bats. These forms are viviparous, nourishing their 

 larvae within the uterus of the female. The newly deposited larva 



Fig. 326. Early stages of the Diptera. A, Larva oi Musca domestica. Acephalous 

 amphipneustic type. B, Empty puparium of Musca domestica. C, Pupa of 

 Musca domestica removed from puparium. D, Larva oiBibio sp. Eucephalous 

 peripneustic type. A, B, and C after Hewitt; D, original, sp. spiracle. 



at once pupates, hence their inclusion in the group Pupipara. Among 

 muscid Diptera the tsetse flies are similarly viviparous. 



The eucephalous larva develops into an exarate pupa from which 

 the adult emerges by a longitudinal slit on the thorax. The pupa 

 resulting from the acephalous larva, on the other hand, is coarctate,the 

 last larval skin being retained as a protective puparium. The latter 

 splits transversely to allow the adult to emerge (Fig. 326 C). 



