STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 505 
gence from the pupal case, and at this time they may be seen 
copulating. 
1. The copulation of M. domestica appears to have 
been first described by Reamur (1738). It has been carefully 
described recently by Berlese (1902), whose observations my 
own confirm. ‘I'he male may perform a few tentative opera- 
tions before copulation takes place, and these have been mis- 
taken for the actual act. The male alights on the back of 
the female by what appears to be a carefully calculated leap 
from a short distance, and this act seems to indicate a faculty 
on the part of the fly of being able to judge distance. It 
then caresses the head of the female, bending down at the 
same time the apical portion of the abdomen. ‘The male fly 
is, however, peculiarly passive during the operation, its influ- 
ence apparently being only tactual, it is only when the female 
exerts her ovipositor and inserts it into the genital atrium of 
the male that copulation can successfully take place. When 
the ovipositor has been inserted into the genital atrium of the 
male, the accessory copulatory vesicles of the female become 
turgid and retain the terminal segment in this position, in 
which the female genital aperture is situated opposite to the 
male genital aperture at the end of the penis, the latter 
depending from the roof of the genital atrium. (This will be 
better understood by reference to the figures of these parts 
in Part I of this Memoir). The attachment of the penis to 
the female genital aperture is made still firmer by the dorsal 
sclerites of the eighth segment of the female and the ventral 
sclerites of the seventh segment, the so-called secondary for- 
ceps of the male acting respectively above and below the 
penis. The fifth ventral segment, or primary forceps of the 
male, assist the accessory copulatory vesicles of the female in 
preventing the withdrawal of the ovipositor before the sper- 
matozoa have been injected into the female genital aperture, 
by which way they enter the spermathece. The whole act 
may be over in a few moments or they may remain in coitu 
for several minutes. 
The eggs are laid a few days after copulation; I found 
