INO:2.|| ANURIDA MARITIMA. 273 
of the embryo has proceeded much farther. The continuous 
mesoderm sheet separating the germ cells from the yolk mass 
has been broken; at the most curved part of the mass of germi- 
nal cells there is direct communication between them and the 
yolk. Whether this breakage is due to rapid flexure or rapid 
increase in the number of germ cells, which show evidences of 
frequent division or to both causes, one thing is clear, that the 
germ cells are now in close contact with the yolk. 
Returning now to a consideration of Fig. 50, the fate of germ 
cells originating in the second way may be seen in the series 
shown in Figs. 50 and 54-56. The single cell, set free on the 
outer side of the somite, increases to an irregular mass that lies 
in part sunk into the mesoderm and in part projecting out 
towards the yolk. These cells, at first a solid group, migrate 
outwards and begin to mingle with the yolk (Fig. 54, y.), the 
migration being most noticeable in the outer cells, those nearest 
the yolk. In Fig. 55 migration has not gone so far and the 
greater magnification shows the peculiarly “succulent” char- 
acter of the cells. In Fig. 56, illustrating the extreme result 
of the process, the cells have divided into two groups, one (s,¢.c.) 
remaining near the mesoderm and by repeated divisions increas- 
ing to a large mass of small cells, another (.¢.c.), which has 
migrated out and is spreading through the yolk, still maintain- 
ing, however, a certain relation to the stationary cells. Unfor- 
tunately, in spite of the most careful search, the latest embryonic 
forms found do not seem to supply the next step. The final 
result is seen in the figures in Pl. XXV, Fig. 64 concluding this 
series. This represents a longitudinal slightly oblique section 
of a just-hatched animal, showing the reproductive organs of 
one side of the body. At g.e. is a somewhat irregular mass of 
cells forming the germinal epithelium, lying in the second and 
third abdominal segments. Below this, and directly connected 
with it, is a large irregular sac filled with yellow material, in 
which are scattered a few large cells. Two lobes of this sac are 
cut through, and at its lower end, coming from the hinder end 
of the fifth abdominal segment, is an-ectodermic invagination, 
the duct of the reproductive organs leading to the exterior. 
This animal is recognizably a young male, the parts described 
