ORGANIZATION AND CELL-LINEAGE OF ASCIDIAN EGG. 33 
work of Seeliger, Samassa, and Castle, in distinguishing the dorsal and ventral faces 
in the pregastrular stages. This is due to the fact that the cells at these two poles 
are of somewhat similar shape, size and arrangement, as may be seen by referring 
to figures 117, 118, 120, 124, 130 and 131 of this paper. However, the differences 
between these poles are so marked that there never need be any confusion regard- 
ing them. 
(1) The most striking difference between the two poles is found in the fact 
that at all stages of the cleavage and gastrulation one pole is rich in protoplasm, the 
other rich in yolk. This is particularly noticeable in Cynthia and Molgula, but is 
also true of Czoza, though in this genus the differences between the two poles are not 
Fres. XIII-X VI.—Camera drawings of entire eggs of Ciona intestinalis viewed as transparent objects ; 
gs. XIII and XV are seen from the posterior pole; Figs. XIV and XVI from the leftside. Figs. XIII 
and XIV represent а 44-cell stage passing into а 62-cell stage; Figs. XV and XVI a 76-cell passing into a 
110-cell stage. The position of the equator, the boundary between protoplasm and yolk and the segmen- 
tation cavity are represented as in the preceding figures. In Fig. XIV the cells A7-4 and A7 are neural 
quite so marked as in the other genera named. This difference is so great that in 
properly stained eggs one can always tell at a glance which is the yolk pole and 
which the protoplasmic. In eggs stained in piero-haematoxylin the protoplasm 
is red or light purple, the yolk yellow and the two poles are so unlike that 
5 JOURN. A. N. 8. PHILA., VOL. XIII. 
