1873.] 143 [Packard. 



of Stomoxys calcitrans 1 (Fig. 10, dorsal; and 10 a, ventral view of an 

 immature puparium, in which the pupa is very rudimentary, the ab- 

 domen being continuous with the thorax) that it is difficult to give 

 any characters by which to separate them. The two most impor- 

 tant ones are the following; the anal spiracles of Musca domestica 

 (Fig. 9) are larger, much closer together, square on the opposing 

 faces, and depressed in the middle, while those of Stomoxys calcitrans 

 are remote, round, and flat topped. (10 c.) The lower side of the 

 end of Stomoxys is darker and much more rugose, owing to trans- 

 verse ridges, than in Musca, where it is comparatively smooth. Fig. 

 10 & gives an idea of these ridges and transversely oval enclosures. 

 The ridges lying between the spiracles and the region of the prop- 

 less are wanting in Musca domestica. 



In both genera the prothoracic spiracles of the pupa connect with 

 similar projecting, slightly twisted, long acute points which are situ- 

 ated on each side on the hinder edge of the metathoracic segment of 

 the puparium. These stigmata are not represented in either of the 

 drawings of the puparia we here present. The divisions of the pro- 

 thoracic stigmata in the puparium of Stomoxys are five in number. 

 The puparia of this species occurred more abundantly with us than 

 those of the Domestic Fly, and were at first mistaken for them. The 

 puparium of M. domestica may at once be distinguished from Cal- 

 liphora and Sarcophaga by the obtusely pointed (compared with 

 those of C. vomitoria and S. carnarid) end, and the full rounded hind 

 end, with the spiracles externally like buttons ; also by its smaller 

 size, and by the double row of large granulations, while in Calliphora 

 and Sarcophaga there are twelve or more. 



In Musca, as well as in Stomoxys, when the pupa is formed, the 

 hard frame work of the jaws of the larva rest next to the skin of the 

 puparium, and always on the ventral side, and apparently in connec- 

 tion with the old larva skin. When the fly pushes its way out of the 

 pupa case, the anterior end of the latter splits off just behind the su- 

 ture between the metathoracic and first abdominal segment. And 

 often when the front end of the puparium is forced off, the ventral 

 half, with most of the rudiments of the mouth-parts, remains attached 

 to the case. 



A parasite found in the puparium of Musca domestica will be de- 

 scribed at the end of this essay. 



1 As has been noticed by Bouche" (I. c, p. 56) as regards the larval state. 



