214 BULLETIN : MUSEUM OF COMPAKATIVE ZOOLOGY. 



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 reageut. 



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 ceil 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 structureless 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 



