ON Till'; ANATOMY OF HISTRlOBDEf.LA HOMAKI. 331 



wliicli lies between the two lateral halves of the org'an. 

 During life this is always full of vei'y actively moving 

 spermatozoa. 



The penis is a firm, semi-solid, peai'-shaped body, the 

 pointed end being directed backwards. It is always carried 

 retracted within the sheatli. Unlike Stratiodrilus, it is 

 not composed of black chitiuous material similar to that of 

 the jaws, but of some transparent substance, sufficiently 

 rigid, however, to enable its being driven through the firm 

 cuticle of the female in the act of copulation. It is pro- 

 truded through the quadrilateral-shaped mouth of the penis- 

 sheath by the action of the strong pi-otractor muscles. The 

 organ itself is composed of two lateral blades, the spermatozoa 

 being ejected through the median canal between them during 

 copulation. 



In relation with the dorsal surface of the penis on either 

 side, and taking up the lateral posterior corners of the 

 generative region, are the so-called accessory glands of the 

 penis (figs. 11 and 40). These are large vacuolated groups 

 of cells forming oval masses running up to the dorsal surface 

 on either side of the gut. From each gland a small duct 

 leads down to the penis, and is inserted laterally about its 

 middle. This opens into the canal on the penis on its ventral 

 side. The gland-cells are divided into an anterior and pos- 

 terior group. In horizontal sections the gland appears as a 

 four-lobed structure, posterior and dorsal to the base of the 

 penis. The anterior and smaller of these groups is composed 

 of numerous cells, while the posterior, although larger, consists 

 of fewer cells. The cytoplasm is granular and very vacuolar. 

 This is shown in figf. 40, where their anterior ends come in 

 the section on either side of the gut. In transverse section 

 the gland will be seen to be composed of two groups of 

 cells, one of which is much smaller and more dorsal than 

 the other. This is wedged in against the gut on either side. 

 Towards the posterior region of the gland the cells are 

 somewhat larger. The largest of these contains a vacuole 

 of considerable size. This probably acts as a receptacle for 



