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ORGANIZATION AND CELL-LINEAGE OF ASCIDIAN EGG. 13 
Van Beneden and Julin (1884, pp. 4 and 5) call attention to the fact that 
Corella parallelogramma produces two kinds of eggs, one yellow the other gray in 
color. Both kinds of eggs develop normally and in the same manner and give rise 
to larvee, the endoderm cells of which are colored yellow or gray. С/аге ла risso- 
ana also produces two differently colored kinds of е; ggs, one pure rose the other 
yellowish in tint. All eggs produced by the same individual have the same color. 
In the species of C/ave//zna studied by Seeliger (1885) the color of the proto- 
plasm surrounding the nuclei of the cleavage cells is yellow, as an inspection of his 
figures of the living eggs shows (v. his plate I). 
These cases, taken in conjunction with my observations on the eggs of Cynthza, 
Ciona, Molgula and Boltenza, show that the eggs of ascidians are frequently 
colored ; these colors are usually found in the yolk, and in the later development 
pass into the endoderm cells. In Сумійга the peripheral layer is also colored, and 
this fact leads me to hope that some other ascidian may be found in which still 
other portions of the oóplasm may be differentially colored. 
II. MATURATION AND FERTILIZATION. 
These processes are so intimately associated in the ascidian egg that it is diffi- 
cult and perhaps inadvisable to treat them entirely separately. As in so many 
other eggs the entrance of the spermatozoon furnishes some stimulus to the egg 
which leads to the completion of the maturation divisions. Without this stimulus 
the egg may remain in the stage of the metaphase of the first polar spindle for 
hours or even days. 
А. MATURATION. 
1. Disappearance of Nuclear Membrane. 
The first steps in the formation of the polar spindle take place before the 
entrance of the spermatozoon. Almost as soon as the egg is laid, and sometimes 
even before this, the wall of the germinal vesicle dissolves and the clear protoplasm 
contained within the germinal vesicle moves up to the animal pole of the egg where 
it may spread out into a сар or peripheral layer (Czoza), or may form merely a 
somewhat flattened disk (Султа). As soon as the nuclear membrane has dis- 
solved the chromosomes, nucleolus and a granular mass from which the spindle 
fibres are formed gather together into the center of this area of nuclear proto- 
plasm (figs. 62, 63, 77, 78); since the chromosomes lay at the periphery of the ger- 
` minal vesicle before its membrane dissolved, this involves a considerable movement 
on the part of these various constituents. Хо distinct linin network is visible 
throughout the germinal vesicle, either before or after its membrane dissolves, and 
the drawing together of these scattered elements into a central mass must be due 
to something other than the contraction of the threads of such a network. 
The chromosomes, when drawn together into a central mass, are connected by 
a faintly staining, finely granular substance, which is much denser than the sur- 
rounding nuclear protoplasm. In the further development of the polar spindle this 
mass gives rise to the spindle fibres, and from this fact, as well as from its staining 
reactions, it may be identified with linin (figs. 62, 77). 
