HARGITT: PENNARIA TIARELLA AND TUBULARIA CROCEA. 205 
ruptured. A large centrosphere with astral radiations is present, 
but no central body could be found. Cytoplasmic division is con- 
siderably delayed, the second nuclear division being finished before 
the first cleavage furrow has cut half through the egg. 
B. 'TUBULARIA CROCEA. 
1. Odcytes.— The primordial germ cells divide mitotically to 
form the odgonia, and the latter by mitosis give rise to the odcytes. 
The daughter chromosomes resulting from the last odgonial division 
lose their individuality, and at this time occurs a differentiation into 
food cells and egg cells. In the former the chromatin of the nucleus 
becomes scattered in large granules along a delicate linin reticulum, 
which is limited to the outer half of the nucleus, but is connected by 
linin fibres with the central nucleolus. ‘These cells have not, perhaps, 
lost their power of becoming egg cells, but most of them serve as food 
for other odcytes. In the odcytes which form egg cells at once, the 
chromatin forms a definite spireme, which gives rise to more or less 
distinct loops. ‘The loops assume a definite polar arrangement, their 
open ends being attached to the nuclear membrane. ‘This apparently 
represents the synapsis stage, and reduction of chromosomes seems to 
occur at this time, though how the reduction is actually accomplished 
could not be determined. 
a. Germinative vesicle.— The polar arrangement of the chromatin 
is soon lost, and the odcyte begins to grow rapidly. ‘The loops become 
granular and more delicate and may undergo a longitudinal splitting, 
but the evidence on this point is too scanty to allow any conclusions 
to be drawn. As growth continues the germinative vesicle shows no 
further sign of chromatin loops, and toward the end of growth exhibits 
only a mass of fine granules which select plasma stains. 
b. Nucleolus— The nucleolus of the odcyte is plasmatic at all 
times. It increases in size for a short time in the young oécyte (per- 
haps by the absorption of nuclear sap), but as soon as the oécyte begins 
to grow the nucleolus may begin to decrease in size, or this decrease 
may not begin till a much later period. ‘This decrease is accomplished 
in two ways: (1) Liquid substances pass out of the nucleolus and along 
the linin reticulum to become incorporated in the reticulum, presum- 
ably with the chromatin; (2) actual fragmentation may occur in the 
early stages, and in the later growth it always occurs. ‘The fragments 
either dissolve in the nuclear sap or become arranged along the nuclear 
reticulu'- and are eventually transformed into, or absorbed by, the 
