214 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
to have been for the larval stages the best reagent which I employed. 
Davidoff's corrosive-acetic mixture, which has been much used of late by 
workers on ascidian embryology, is in my experience less faithful in its 
preservation than Perenyi's fluid, for it shows a tendency to swell certain 
structures, and lacks the instantaneous hardening effects of that reagent. 
2. Decortication, Staining, Mounting. 
The egg of Ciona is surrounded by a series of egg membranes, a cor- 
rect idea of which is given by the figure of the mature egg of Ascidia 
canina, reproduced after Kupffer (72) in Korschelt u. Heider’s “ Lehr- 
buch d. vergl Entwicklungsgeschichte,” Figure 736. The egg cell is 
seen to be surrounded by a clear space — probably occupied by jelly — 
bounded by the test cells, which are arranged in a rather compact layer 
one cell deep, so that they seem almost to form an epithelium under- 
neath the chorion. The chorion is a structüreless transparent mem- 
brane, upon which, as on a basement membrane, the follicle cells 
(*Schaumzellen ") rest. In the egg of Ciona, after it is thrown out 
into the water, these highly vacuolated cells are even more conspicuous 
than in the egg of Ascidia as figured by Kupffer. They extend out 
radially about twice. as far as indicated by Kupffer's figure, forming a 
sort of halo round the egg. The highly refractive nuclei are carried out 
to the pointed outer ends of the tapering follicle cells. 
The presence of the follicle cells and test cells did not interfere 
seriously with the study of the early stages of cleavage in the living egg, 
since the clear space between the egg cell and the layer of test cells 
allows one, with a sufficiently strong illumination, to make out perfectly 
the outline of the blastomeres and sometimes even nuclear figures in 
them. But upon preservation in alcohol the envelope formed by the 
test cells, chorion, and follicle cells collapses, obliterating the clear space 
and becoming closely applied against the egg cell, thus forming a very 
serious obstacle to the study of the egg as a whole object. This obstacle 
I was able to remove by following in a modified form a very ingenious 
method devised by Chabry (’87, p. 169) for the removal of the follicle 
cells from the living egg of Ascidiella. a process which he called “ decor- 
tication.” It consisted in simply sucking the eggs into a fine capillary 
glass tube too small to admit the eggs without the removal of their 
follicle cells, yet large enough to allow the passage uninjured of the egg 
itself, 
In applying this method to preserved material, I first stained the eggs, 
as a rule, so that they might be more easily seen. Upon transferring 
