34 ORGANIZATION AND CELL-LINEAGE OF ASCIDIAN EGG. 
there can be no excuse for mistaking them. In CyzzAza, indeed, these differences 
can be easily recognized in the living egg, the yolk being slate-gray and the proto- 
plasm colorless or yellow (figs. 28, 32, 37,38). The yolk spherules are not scattered 
through the cytoplasm, but the limits of the yolk and cytoplasm are sharp and dis- 
tinct. In the cells at the yolk pole the cytoplasm is limited to a small area around 
the nucleus; at the protoplasmic pole the cytoplasm occupies a large part of the 
cell, the yolk being limited to the inner ends of the cells. This is seen especially 
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II-X X.—Actual sections of eggs of Cynthia гечи: Figs. XVII and ХІХ in the median 
plane, Figs XVIII and XX in a transverse plane igs. : and XVIII represent а 90-94 cell stage; 
l n p osely 
crowded spheres, : The clear protoplasm 
is located chiefly in the cells of the animal half of the egg ( n escent 
cells (mesoderm) ( B5-?, B®?, B3) and neural plate тан Bree “ күре balf of A5?) of the lower еее 
Тһе remaining cells of the lower hemisphere, (end r, B6, A6, A6٠3, and chorda, A73 and lower 
half of A52) are filled with yolk ; yolk is also found tA "the uiu ends of all the other cells. The асту 
protoplasm is limited e crescent cells and to а single pair 9 5 of the upper hemispher е (5-3), In 
xim 
animal pole are flatter, Lite 4 owing to the fact that they oe dividing: in көзү ХІХ апа XX the cells 
at the animal pole are columnar, those at the vegetal pole flattened. The polar bodies are actually pres- 
ent where they are represen ied 
well in actual sections taken in the egg axis; such sections are shown in text figures 
XVII to XXIV, and it can there be seen that the cytoplasm is largely found in those 
cells which lie on that side of the egg where the polar bodies are found, while the 
cells at the opposite pole are Ише entirely filled with yolk. These yolk-laden 
