19 ORGANIZATION AND CELL-LINEAGE OF ASCIDIAN EGG. 
from Green Turtle Cay, Bahamas. What may perhaps be the same layer was de- 
scribed by Kowalevsky (1866) as a “gelatinous layer,’ in which the test cells are at 
first imbedded ; later, about the time of the first cleavage, the test cells move to the 
periphery of this layer. In these respects this gelatinous layer of Kowalevsky re- 
sembles the peripheral layer of protoplasm, but in other respects the differences 
are very great; for example, Kowalevsky says that this layer is formed by the 
activity of the follicle cells, that it closely surrounds the blastomeres during cleav- 
age, and that it becomes the gelatinous mantle of the adult, while the cells within 
it (test cells) form the cells of the mantle. In none of these respects is this gela- 
tinous layer like the peripheral layer of protoplasm described above, and I am in 
doubt whether Kowalevsky actually saw this layer of protoplasm or whether he is 
not describing the perivitelline space between the surface of the egg and the chorion. 
It is interesting to note that Kowalevsky calls especial attention to the yellow color 
of the test cells, though he nowhere indicates that he has seen any such yellow 
pigment in the egg itself. Kupffer (1870), on the other hand, concluded that the 
test cells were formed by free cell formation from the substance of the egg, because 
“die Zellen gleich Anfangs genau die Farbe des Dotters haben" ; however, he 
nowhere indicates that the peripheral layer of the egg differs in any way from the 
remainder. In not one of the many later papers on the ascidian egg can I find any 
reference to this peripheral layer of protoplasm, except in that of Morgan already 
referred to. In view of the ease with which it can be seen, both in living and in 
stained material, and of the very important part which it takes in development, 
this is most remarkable and inexplicable. If due attention had been given to this 
feature of the ascidian egg, it is safe to say that some of the most conflicting accounts 
of ascidian embryology would never have been written. 
А peripheral layer of protoplasm, entirely similar in structure to that of the 
ascidian egg, has been observed and described by Sobotta (1897) in the egg of Am- 
phioxus. In this case Sobotta says that the peripheral layer gives rise in large part 
to the inner egg membrane, which forms about the time of the maturation, but even 
after the formation of this membrane a portion of this layer may remain at the 
periphery of the egg. Sobotta speaks of the desirability of observing this layer in 
the living egg, and from what I have seen in the ascidians I can but emphasize this 
suggestion. In the ascidians this layer does not disappear with the formation of the 
egg membrane, to which it contributes, but collects at the lower pole when the 
egg is fertilized; from Sobotta’s figures I judge that the same thing happens in 
Amphioxus. 
The colors of ascidian eggs deserve some notice at this place. In 1870 
v. Kupffer observed in the living eggs of Ascidia canina (Ciona intestinalis ?) that 
in the early stages of the ovarian egg the odplasm is yellow ; later, as the egg ripens, 
this color changes to a brownish red (Kupffer, 1870, p. 10). In the later stages of 
development this red color is limited entirely to the walls of the alimentary tract. 
In different animals and at different periods of the year Kupffer found that this 
color varied from a bright red to an orange tone (p. 17). 
