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 h^s been deter- 

 mined by observation in the living insect, the relation of the 

 parts, even in slightly oblique sections, is not difficult to 

 interpret. 



