BY JAS. P. HILL. 29 



the branchial region, as is characteristic of the genus Plychodera, 

 the gonads only exist laterally to the gill pores, and consist of 

 dorsal and ventral gonad branches which are each again sub- 

 divided into lesser lobes : the dorsal usually into two long lobes 

 which occupy the uppermost portion of the cavity of the genital 

 wings, the ventral into a number (3-4) of shorter and smaller 

 lobes. 



In the genital region proper, as in Pt. ckivigera, each gonad 

 consists of three main branches: (1) a dorsal (figs. 22, 23, cbjb.) 

 occupying, as in the branchial region, the dorsal part of the cavity 

 of the "genital wings," and divided into two long lobes or in some 

 cases into two long lobes and one short one; (2) a ventro-lateral 

 Ijranch situated on the outer side of the lateral septum, between 

 it and the outer body wall, and also subdivided into two lesser 

 lobes (figs. 22, 23, vgh.)', (3) a median lateral branch occupying 

 the cavity of the dorsal chamber of the trunk coelom, enclosed by 

 the lateral septum and extending in it alcove the gut towards the 

 median dorsal line (figs. 22, 23, mg.). This median ventral 

 branch is also subdivided into two. In this species, then, there 

 are in connection with each genital pore at least six lesser 

 branches. In fig. 23, a section from about the middle of the 

 genital region is represented which has passed through one of the 

 genital pores {gap.) filled up by a mass of spei-matozoa. The 

 specimen from a series of which this section is taken was preserved 

 while in the act of extruding the ripe spermatozoa in the form of 

 whitish filmy masses. 



Structure of Gonads : According to 8pengel the wall of the 

 gonads consists of three layers — an outer peritoneal layer, a middle 

 limiting membrane and an inner germ layer. The outer peritoneal 

 la3^er is in my preparations very indistinct, and represented by 

 some small flattened nucleated cells"' more or less remote from 

 each other and closely applied to the middle limiting membrane. 

 In the latter there is situated a well marked blood sinus. I have 

 never been able to observe a layer of longitudinal muscles in the 

 wall of the gonads in this species. Also, I have not been able to 

 distinguish the germ layer as a distinct layer, but certain small 



