STEUCTURE, DEVELOPMENT, AND EIONOMICS OP HOUSE-PLY. 3S1 
head of S. calcitrans; this larva measured 1‘6 to 2 mm. iu 
length. Generali (1886) described a nematode from the 
common fly, which he calls N^ematodum spec. It is 
highly probable, as my friend Dr. A. B. Shipley has suggested 
to me, that Generali^s nematode and the F. muscm of Carter 
are identical. Diesing (1861) created the g’enus Habronema 
for the Filaria muscae 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. 
Out 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 tlie figures of 
the latter I feel convinced that their specimens and mine are 
the same species, called by Diesing Habronema inuscae 
(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 papillae 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 
moi’e than the anterior end aud terminates in a small dilated 
extremity, which is covered with minute sjiines (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 aud the cephalic air-sacs, from which position they 
