487 



elongated ovary and arranged along either side of it a series of testi- 

 cular masses. The ducts of the latter unite on the inner free surface 

 of the ovary to form a common vas deferens. The vas deferens and the 

 oviduct open near each other at one end of the gonad (see Fig. V, 3). 

 It will be most suitable to speak of each of the testicular masses as a 

 testis, of their ducts as vasa efferentia and of the common duct as the 

 vas deferens. The primitive position of the testes appears to have been 

 in the angle (as seen in a transverse section of the gonad) between the 

 ovary and the body wall. In Pelonaia corrugata (see Fig. Ill for a 



P elonai a. corrugata. 



Gon.ioCa.rpa. cor iacea 



Goni o carpa rustica 



Fig. III. Diagrammatic transverse sections of gonads. 



transverse section) there has been only a slight departure from this pri- 

 mitive condition. 



There are apparently no species in which this original condition 

 has been retained (?). There have been two directions of change from 

 this condition. 



In the first case, exemplified by Dendrodoa, Pandocia and Cnemi- 

 docarpa, the testes have extended in between the ovary and the body 

 wall, as is shown in Fig. II. They have at the same time become more 

 or less lobed. The gonad varies in its relation to the body wall and 

 this affects its shape. These differences appear to be of slight value 

 only. In perhaps the majority of cases the gonad is closely applied to 

 the wall as in Pandocia fibrosa (see Fig. II). This is the condition in 

 Dendrodoa and also in Cnemidocarpa mollis. In these the transverse 



