BY JAS. P. HILL. 
29 
the branchial region, as is characteristic of the genus Ptychodero, 
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 Pi. clavigera, each gonad 
consists of three main branches: (1) a dorsal (figs. 22, 23, dyb.) 
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 
branch 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, vgb.); (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 above the gut towards the 
median dorsal line (figs. 22, 23, my.). 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 spermatozoa. 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 Spengel 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 
laj^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 
