THE EXTERNAL GENERATIVE ORGANS. 747 
must be, therefore, an open question to which somite these 
scales belong. I regard them as modified ventral appen- 
dages. They either represent the gonapophyses of the pro- 
genital somite, of the undeveloped mesogenital somite or 
they may possibly be the representatives of the anal cerci. 
The vaginal orifice when at rest is apparently closed, so that 
it is not easy to see that any opening exists between the 
ventral plates of the anal and progenital somites. It is only 
when an egg is actually passing that it is possible to deter- 
mine the position of the vaginal orifice in the living insect. 
I determined its position by observing the deposition of the 
eggs by the aid of the microscope. This is easily accom- 
plished by decapitating an egg-laying female and fixing it so 
that the passage of the eggs can be observed. This continues 
uninterruptedly in the decapitated insect. 
It is not easy to prepare sections which show the orifice 
of the sexual canal distinctly, owing to the invagination of 
the ovipositor; but when once its position has been deter- 
mined by observation in the living insect, the relation of the 
parts, even in slightly oblique sections, is not difficult to 
interpret. 
