LIFE-HISTORY OF BUCKEPHALUS HAIMEANUS. 64.9 
sporocysts that I have been able to positively identify as such. 
In many oysters I found in the palps and gonads and entan- 
gled in the gills little cysts, which, when examined alive, 
seemed to consist of a simple sac enclosing a few cells. 
Until I had sectioned and stained some of these bodies I felt 
inclined to consider them as very young sporocysts, only 
shortly removed from a miracidium-like larva. Their appear- 
ance in sectioned material causes me to doubt this interpre- 
tation (fig. 12). 
THe ORIGIN OF THE GERM-CELLS. 
The origin of the germ-cells, from which the larval forms 
Trematodes arise, has been discussed at considerable length 
by various investigators. Leuckart (34, 1882) and Schwartz 
(35, 1886) trace them directly to the egg. Wagener (36, 1866) 
and Biehringer (87, 1884) describe their origin from the 
body wall. Thomas (38, 1883) thinks that the germ-cells may 
originate in either or both of these ways. 
In B. haimeanus there is little doubt that the germ-cells 
arise in the wall of the sporocyst. 
Figs. 6, 7, and 17 illustrate conditions frequently seen in 
the younger portion of the germ-tubes. In the growing end 
of the tube (fig. 7) the outlines of the cells which compose 
the walls are easily seen. These cells have lightly staining 
rather granular cytoplasm and a vesicular nucleus with scat- 
tered deeply staining nucleoli. 
In the older portions of the tube the original cell boundaries 
have disappeared. ‘The cytoplasm of these cells has appa- 
rently collected itself in dense, granular, rounded masses 
around the nuclei, the resulting structures, as their subse- 
quent fate shows, being the germ-cells (fig. 7,g.c.) Scattered 
about within the wall are a few nuclei, which have retained 
their original appearance. 
The germ-cells now pass from their place of formation 
into the lumen of the tube. In the great majority of cases, 
so far as I have been able to determine, there is no division 
