DEVELOPMENT OF ELASMOBRANCH FISHES. 5 



While, then, there are on the one hand Oellacher's observa- 

 tions on a single animal, hitherto unconfirmed, there are on the 

 other very definite observations tending to shew that the ger- 

 minal vesicle has in many cases an altogether different fate. 

 Gotte^ not to mention other observers before him, has in the 

 case of Batrachian's eggs traced out with great precision the 

 gradual atrophy of the germinal vesicle, and its final absorption 

 into the matter of the ovum. 



Gotte distinguishes three stages in the degeneration of the 

 germinal vesicle of Bombinator's egg. In the first stage the ger- 

 minal vesicle has begun to travel up towards the surface of the 

 egg. It retains nearly its primitive condition, but its contents 

 have become more opaque and have partly withdrawn them- 

 selves from the thin membrane. The germinal spots are still 

 circular, but in some cases have increased in size. The most 

 important feature of this stage is the smaller size of the germi- 

 nal vesicle than that of the cavity of the yolk in which it lies, 

 a condition which appears to demonstrate the commencing 

 atrophy of the vesicle. 



In the next stage the cavity containing the germinal vesicle 

 has vanished without leaving a trace. The germinal vesicle 

 itself has assumed a lenslike form, and its borders are irreofular 

 and pressed in here and there by yolk. Of the membrane of 

 the germinal vesicle, and of the germinal spots, only scanty 

 remnants are to be seen, many of which lie in the immediately 

 adjoining yolk. 



In the last stage no further trace of a distinct germinal 

 vesicle is present. In its place is a mass of very finely granular 

 matter, which is without a distinct border and graduates into 

 the surrounding yolk and is to be looked on as a remnant of 

 the germinal vesicle. 



This careful investigation of Gotte proves beyond a doubt 

 that in Batrachians neither the membrane, nor the contents of 

 the germinal vesicle, are extruded from the egg. 



In Mammalia, Van Beneden^ finds that the germinal vesicle 

 becomes invisible, though he does not consider that it abso- 

 lutely ceases to exist. He has not traced the steps of the process 



^ Enhcicldiingsgeschichte dor Unke. 



^ Efcherches sur la Composition et la Signification de VCEuf. 



