Chap. XIII.] THE COCKROACH. 275 



micropyles, or minute holes for the admission of spermatozoa 

 from the spermatheca. 



(2.) In the Male. On dissecting an adult male cockroach a 

 curious "mushroom-shaped gland" (83, B.) is seen situated at the 

 end of a short duct. This organ was for long regarded as the 

 testis, since in the adult it contains developing spermatozoa. 

 The true testes are liable to be missed, since they are only func- 

 tionally active in the very young cockroach, becoming reduced, 

 though they are not altogether obliterated, in the adult, in 

 which they are vesicular bodies (83, B., ts.) lying beneath the 

 fifth and sixth terga. Vasa deferentia (v. d.) pass from them into 

 the coalescent cavities of the mushroom-shaped gland, or vesiculce 

 seminales, which bear a number of longer and shorter finger-like 

 processes, the utriculi major es and breviores (u. m., u. b.). The 

 epithelium of the testis in the young cockroach gives rise to 

 sperm cells, which develop into hollow spermatocysts, around 

 which spermotoblasts are placed radially. These are converted 

 into spermatozoa. The later stages of the development of sper- 

 matozoa are, however, carried on in the vesiculse seminales and 

 their utricles, when the testes have become reduced. The sper- 

 matozoa pass from the vesiculse seminales by an ejaculatory duct 

 (d. e.), by which they are carried out of the body. A subsidiary 

 gland of unknown function lies on the ventral surface of the 

 ejaculatory duct. 



Development. The segmentation of the ovum in insects is 

 on the centrolecithal system, as in the crayfish. The first 

 segmentation nucleus undergoes division in such a way that a 

 layer of cells forms a superficial blastodermic layer, while other 

 yolk-cells remain scattered through the central mass. 



In the blastodermic layer an elongated ventral plate is formed, 

 in which the embryo begins to be developed. This broadens at 

 the anterior end ; further back it is transversely divided into 

 segments, of which the total number seems to be seventeen. 

 Indications of the appendages appear early, limb-buds being 

 formed, according to recent observers, on all the abdominal seg- 

 ments. These subsequently disappear. 



