44 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



opens behind its base in front of the labium (fig. 23, SIO). The fe- 

 male of the mosquito and other adult Diptera possesses a free hypo- 

 pharyngeal stylet, but it is traversed by the salivary duct. According 

 to Thompson (1905) the hypopharynx of the female mosquito is 

 differentiated by cellular growth from the median line of the anterior 

 (lower) surface of the labium during the pupal stage. Since the 

 hypopharynx, when it becomes a free stylet, contains the salivary 

 duct, it would seem that in its separation from the labium it must take 

 a part of the labium with it. In the male the hypopharynx is not 

 separated from the labium, and the salivary channel remains in the 

 labium. Dimmock (1881) says that in the male of Culex "the hypo- 

 pharynx is, throughout its whole length, joined to the labium," and 

 Hurst (1890) observes that it is "inseparable from the labium." 



The fact that the hypopharynx of Diptera contains the salivary 

 duct has given rise to the idea that this stylet is a new formation not 

 homologous with the hypopharynx of other insects (see Demerec, 

 I 95°> PP- 375, 376) . Yet the stylet in Diptera has all the usual rela- 

 tions of the hypopharynx to surrounding parts, and its base forms 

 the floor of the preoral cibarial pump (fig. 24 E), just as in the 

 cockroach (fig. 23) and other generalized insects. 



The cuticle of the pupal mouth parts represents the organs as 

 they are developed in the pupa. Inside the cuticular sheaths a renewed 

 growth of the epidermis produces the final adult form of the stylets, 

 just as the adult legs are formed within the cuticle of the pupal legs 

 (figs. 15 G, 17 A). The segmented maxillary palpus of the adult, for 

 example, is clearly seen inside the simple palpal sheath of the pupa 

 (fig. 15 F, Pip), and within the end of the pupal labium {Lb) are 

 visible the labellar lobes of the adult. 



The thorax. — The large thorax of the pupa is indistinctly seg- 

 mented, but it bears the legs and wings, and carries on its back the 

 respiratory trumpets (fig. 16 A). The legs and the wings of the pupa 

 have been taken over directly from the larva. The legs have increased 

 in length and their joints are more distinct (fig. 17 A), but they are 

 closely folded in loops against the sides of the thorax as in the larva. 

 The mesothoracic wings are much larger and more winglike in shape ; 

 the hind wings are still triangular lobes of the metanotum. Within 

 the cuticle of the pupal appendages are plainly seen the developing 

 appendages of the adult. The venation of the forewing is already 

 laid out (D). Within the hindwing may be seen the club-shaped 

 halter (E, Hit), which, whatever may be its evolutionary history, is 

 not formed in ontogeny by a gradual modification of the wing. 



