Packard.] 140 [Nov. 19, 



to the stigma is greater, and the dark terminal portion longer, than 

 in C. vomitoria. The secondary branches are rather shorter than 

 in C. vomitoria, and the two inferior medio-posterior tracheal twigs 

 (Fig. 3 b) arise behind the posterior commissure. The tracheal twigs 

 of the head are distributed much alike in both genera. 



The length of the freshly hatched larva of M. domestica is .07 inch. 

 It remains in this stage about twenty-four hours. 



The second stage. (Fig. 4.) This stage is signalized by the addi- 

 tion of the prothoracic stigmata. This change must necessarily, 

 though we did not perceive it, be accompanied by a moult of the first 

 larva skin, as in Callipliora vomitoria, according to Leuckart 1 and 

 Weismann (I. c). 



The length of the larva at this stage varies from .15-.17 inch in 

 length. Tt is considerably slenderer than in the first stage. We are 

 inclined to think that this stage lasts from about twenty-four to thirty- 

 six hours. One of these larvae grew .05 inch in twenty-four hours. 



The third stage. As this last stage does not differ from the preced- 

 ing one in any important respects except size, the following descrip- 

 tion will apply to both. 



The larva of M. domestica differs from C. vomitoria in being 

 proportionally longer and slenderer, more regularly conical, the body 

 gradually increasing in width to the end, which is square. The prop- 

 leg is small and inconspicuous as compared with that of the other 

 genus, and cannot be seen from above when the larva is in motion. 

 In Callipliora the body narrows towards the end, the stigmatal hollow 

 is very well marked, with eight large subacute conical tubercles on 

 the elevated edge of the round area, which in life is stuck outwards 

 and upwards, presenting a cup-like hollow, at the bottom of which 

 the stigmata are situated. They are large and tun -shaped, deep 

 testaceous in color, with fine longitudinal whitish stripes ; while in 

 Musca domestica they are black, external, being situated in a very 

 slight depression, and are very conspicuous. 



The anal spiracles in M. domestica (Fig. 5 ; 5 a, still more enlarged 

 spiracle of a younger larva than 5) are rounded, forming about three- 

 fourths of a circle, with the opposing sides square, and a broad dark 

 chitinous ridge, which becomes wider and darker with age. The 

 openings are two, very unequal, the longer one apparently formed by 

 the union of what were probably originally two openings. These 



1 Die Larven zustande der Musciden. Archiv fur Naturgescliichte, 1861, p. 60. 



