ORGANIZATION AND CELL-LINEAGE OF ASCIDIAN EGG. 25 
plasmic fields quite separate. The two spindles are usually parallel to each other 
and are always entirely independent, the poles never being united into a triaster 
or tetraster. 
Sections of two dispermie eggs are shown in figures 94 and 95; in the former 
the sperm nuclei, which have not yet reached the equator of the egg, occupy symmet- 
rical positions on each side of the mid-line, and the protoplasmic field in which they 
lie is located on that side of the egg which corresponds to the posterior pole of nor- 
Fies. III-VI. суие eggs of = partita; drawn from stained preparations of entire 
eggs. Figs. III. and V are viewed from the "vegetal pole, the polar bodies being seen 
through the Me" IV is viewed from the animal pole and Fig. VI from the posterior 
ро undary n the protoplasm and yolk is indi y a crenated line; 
when seen through the egg this boundary is represented by a line of stippl es. 
mal eggs. The yellow protoplasm here forms a continuous crescent, and save for the 
fact that the sperm nuclei do not lie at the middle of this crescent and that a small 
tongue of yolk partly separates the two sperm asters, the egg is not unlike a normal 
one. In figure 95 a later stage of a dispermie egg is shown, in which the sperm nuclei 
have reached the equator and have moved in from the surface toward the center of 
the egg, while one of these nuclei has united with the single egg nucleus. There 
is here also a symmetrical arrangement of the sperm nuclei and of the clear and yel- 
low protoplasm on each side of the mid-line. The protoplasmic areas are here further 
4 JOURN. А. N. S. PHILA., VOL. XIII. 
