196 GERM-CELL CYCLE IN ANIMALS 
by him the “‘besondere Korper,” may be unequally 
distributed between these cells, and that the one 
which procures the larger portion is the progenitor 
of the spermatozoa, the other of the ova. The evi- 
dence for this view is, however, insufficient. 
In Helix both eggs and spermatozoa originate in 
every acinus of the ovo-testis; it is therefore an ex- 
cellent species for the study of the differentiation of 
the sex cells. According to Ancel (1903) the anlage 
of the hermaphroditic gland of Helix pomatia appears 
a few hours before the larva hatches; it consists of a 
group of cells situated in the midst of the mesoderm, 
from which germ layer it seems to originate. It 
soon loses its rounded form and becomes elongate; 
then a lumen appears within it, thus changing it into 
a vesicle whose wall consists of a single layer of cells 
—a true germinal epithelium. Secondary, tertiary, 
etc., vesicles bud off from the single original vesicle, 
forming the acini of the fully developed gland. Cel- 
lular differentiation takes place by the transformation 
of the germinal epithelial cells into male, nurse, and 
female elements. An indifferent epithelial cell is 
shown in Fig. 57, 4; the chromatin granules are con- 
densed to form irregular clumps. Some of these 
indifferent epithelial cells increase in size and give 
rise to indifferent progerminative cells; the chroma- 
tin clumps fuse, forming more or less spherical masses 
(Fig. 57, E). From cells of this sort originate both 
the odgonia and spermatogonia. The progermina- 
tive male cell passes through the stages shown in 
Fig. 57, B—D; part of the chromatin of the progermi- 
