(140) 



STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 381 



head of S. calcitrans; this larva measured 1*6 to 2 mm. in 

 length. General! (1886) described a nematode from the 

 common fly, which he calls Nematodum spec. It is 

 highly probable, as my friend Dr. A. E. Shipley has suggested 

 to me, that Generali's nematode and the F. muscas of Carter 

 are identical. Diesing (1861) created the genus Habrone ma 

 for the Filaria muscse of Carter, and his description is 

 practically a translation of Carter's original description. 

 Piana (1896) describes a nematode from the proboscis of M. 

 domestica, which, in the occurrence of the male and female 

 genital organs in the same individual, he says, resembles 

 Carter's nematode. He finds that at certain seasons of the 

 year and in certain localities it is very rare, while at others it 

 may occur in 20-30 per cent, of the flies. The larva, after 

 fixation, measured 2*68 mm. in length and 0*08 mm. in breadth. 

 It was cylindrical and gently tapering off at the extremities, 

 with the mouth terminal. 



Oufc of the many hundreds of flies which I have dissected I 

 have only found two specimens of this nematode (fig. 18) . From 

 the descriptions given by Carter and Piana and the figures of 

 the latter I feel convinced that their specimens and mine are 

 the same species, called by Diesing Habronema muscaB 

 (Carter). It is linear, cylindrical, tapering gradually towards 

 both ends. The anterior end is slightly rounded, having the 

 mouth in the centre. I am unable to confirm the presence of 

 the four papilla3 which Carter describes as a little distance 

 from the mouth, nor are they figured by Piana. The cuticle 

 is very faintly marked with transverse striations. The 

 common genital and anal orifice is situated at a short distance 

 from the posterior end of the body, which tapers off slighly 

 more than the anterior end and terminates in a small dilated 

 extremity, which is covered with minute spines (fig. 19). My 

 specimens appear to be immature adult forms, not having 

 reached sexual maturity. The species measures 2 mm. in 

 length and 0*04 mm. in breadth. The specimens that I 

 obtained were situated in the head region, between the optic 

 ganglia and the cephalic air-sacs, from which position they 



