INTERNAL GENERATIVE ORGANS OF THE FEMALE. 677 



The Genital Fossae. These remarkable depressions in the 

 dorsal wall of the uterus are probably concerned in the act of 

 copulation. They are fully developed in the female when it 

 emerges from the pupa, and are protected by a thick laminated 

 cuticle. They probably lodge the curved spines of the penis 

 during copulation. Although the distance of this fossa from 

 the vulva is very considerable in the adult female when the 

 ovipositor is exserted, in the young female it lies close to the 

 vulva. The ovipositor is closed up by its joints being with- 

 drawn one within the other, like the tubes of a portable tele- 

 scope, and the vagina is also invaginated in four folds, one within 

 the other, so that the bursa, as the young uterus is termed, 

 opens directly through a very short segment of the vagina by 

 the vulva. 



The Receptacula Seminis. These organs serve as a receptacle 

 for the sperm of the male ; for although Insects have the 

 sexes distinct, the sperm is transferred from the male by a 

 single sexual act to the bursa, or to the receptacula seminis of 

 the female, where it remains for days, months, or even for 

 years before the ova are fertilised. Fertilisation is effected as 

 the ovum passes through the oviduct, so that the actual act of 

 fertilisation is not effected by the union of the sexes. 



In the Lepidoptera, the bursa does not communicate directly 

 with the oviduct, and opens externally by an orifice on the 

 ventral surface of the abdomen, in front of the orifice of the 

 oviduct. The sperm is afterwards conveyed into the oviduct 

 by the spermatic canal, which unites the two cavities. 



In most insects the sperm is preserved in the spermatic 

 capsules, or receptacula seminis. In the Diptera these are 

 always three in number, two on one side, and one on the 

 other. 



In the Blow-fly the receptacula seminis, or spermathecse, 

 are small capsules, which have a long diameter of "z mm., and 

 a short diameter of about '125 mm. There are two on the 

 right side, and one on the left, connected with the uterus by 

 long muscular ducts, one to each capsule. The orifices of 

 these ducts are close together, immediately in front of the 



