286 
Platybdella Anarrhichae 
In the first place, in some cases sperm development to form morulae 
does not seem to take place all over the spermblastophore but only to 
one side of it, the rest being undifferentiated protoplasm; and, in the 
second, the residual protoplasm of the spermblastophore after the 
mature spermatozoa have become detached still appears to contain 
a central nucleus, which, as far as I know, has never been observed in 
the earthworm. What the significance of this nucleus is, I cannot 
imagine, since the spermblastophores move down the vasa deferentia 
towards the ductus ejaculatorii together with the spermatozoa and are 
presumably ejected with them. The chief point here, then, is that the 
spermatozoa are not developed within the chambers of the testes them¬ 
selves, but that the spermatocytes pass down the vasa efferentia, and 
Fig. 9. Platybdella anarrhichae. Successive stages in the development of the spermatozoa. 
A, sperm mother cell (spermatocyte); B. spermatoblast; C, morula; D, fully 
developed spermatozoa; E. a single spermatozoon; n. nucleus; s.b. spermblastophore. 
that development takes place solely in a widened portion of the vas 
deferens, or vesicula seminalis, which occupies the position where one 
expects to find a first pair of testes. 
From each testis proceeds a small duct, the vas efferens, there being 
as many vasa efferentia as there are testes. In this case the vas efferens 
appears to arise within the testis and among its chambers (Fig. 4 v.e.). 
From the posterior testis on each side the vas efferens passes outwards 
and upwards immediately into the vas deferens which in its course 
receives the remaining vasa efferentia. After taking up the last vas 
efferens, each vas deferens dilates enormously to form the vesicula 
seminalis, and, on arriving at the clitellum, where it narrows, from being 
ventral, it turns dorsal and afterwards forwards. On arriving at the 
level of the $ genital aperture it makes a half-turn, and passing over 
