118 F. M. BALFOUR. 



The following is Hertwig's account of the changes in the 

 germinal vesicle. A quarter of an hour after the egg is laid the 

 protoplasm on the side of the germinal vesicle towards the surface 

 of the egg develops a prominence which presses inwards the 

 wall of the vesicle. At the same time the germinal spot develops 

 a large vacuole, in the interior of which is a body consisting of 

 nuclear substance, and formed of a firmer and more refractive 

 material than the remainder of the germinal spot. In the above- 

 mentioned prominence towards the germinal vesicle, first one sun 

 is formed by radial strife of protoplasm, and then a second makes 

 its appearance, whUe in the living ovum the germinal spot appears 

 to have vanished, the outline of the germinal vesicle to have become 

 indistinct, and its contents to have mingled with the surrounding 

 protoplasm. Treatment with reagents demonstrates that in the 

 process of disappearance of the germinal spot the nuclear mass in 

 the vacuole forms a rod-like body, the free end of which is 

 situated between the two suns which occupy the prominence of 

 the germinal vesicle. At a slightly later j)eriod granules may be 

 seen at the end of the rod and finally the rod itself vanishes. 

 After these changes there may be demonstrated by the aid of re- 

 agents a spindle between the two suns, which Hertwig believes to 

 grow in size as the last remnants of the germinal spot gradually 

 vanish, and he maintains, as before mentioned, that the spindle is 

 formed at the expense of the germinal spot. Without following 

 Hertwig so far as this^ it may be permitted to suggest that his 

 observations tend to show that the body noticed by Pol in the 

 median Ihie, on the inner side of his spindle, is in reality a 

 remnant of the germinal spot and not, as Fol supposes, part of 

 the germinal vesicle. Considering how conflicting is the evidence 

 before us it seems necessary to leave open for the present the 

 question as to what ])arts of the germinal vesicle are concerned 

 in forming the first spindle. 



i.^£^ 





V'://. 





P20_ (5_ —Port ion of the ovum of Asterias glacialis, showiup; the spindle 

 formed from the metamorphosed germinal vesicle projecting into a 

 protoplasmic |)rominence of the surface of the egg. Picric acid pre- 

 paration (copied from Fol.). 



' Hertwig's full account of his observations, with figures, in the 4lli vol. 

 of the ' Mor|)hologische Jahrbuch,' has appeared since the above was 

 written. The tigures given strongly su])port llertwig's views. 



