GERMINAL VESICLE. 



ovum two clear spaces (fig. 24), one ovoid and nearer the surface, and the 

 second more irregular in form and situated rather deeper in the vitellus. In 

 the upper space parallel stride may be observed. By treatment with reagents 

 the first clear space is found to be formed of a horizontally-placed spindle 

 with two terminal stars, near which irregular remains of the germinal spot 

 may be seen. Slightly later (fig. 25) there may be seen on the lower side of 

 the spindle a somewhat irregular body, which may possibly be part of the 

 remains of the germinal spot, though Fol holds that it is probably part of the 

 membrane of the germinal vesicle. The lower clear space visible in the 

 fresh ovum now contains a round body, fig. 25. Fol concludes that the 

 spindle is formed out of part of the 

 germinal vesicle and not from the 

 germinal spot, while he sees in the 

 round body present in the lower of 

 the two clear spaces the metamor- 

 phosed germinal spot. He will not, 

 however, assert that no fragment of 

 the germinal spot enters into the for- 

 mation of the spindle. 



The following is Hertwig's (No. 

 92) account of the changes in the 

 germinal vesicle in Asteracanthion. 

 Shortly after the egg is laid the proto- 

 plasm 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 prominence first mentioned as 

 projecting inwards towards the germinal vesicle first one star, formed by 

 radial striae of protoplasm, and then a second make their appearance ; while 

 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 its vacuole 

 forms a rod-like body, the free end of which is situated between the two stars 

 which occupy the prominence indenting the germinal vesicle. At a later 

 period granules may be seen at the end of the rod and finally the rod itself 

 vanishes. After these -changes by the aid of reagents there may be demon- 

 strated a spindle between the two stars, which Hertwig believes to grow in 

 size as the last remnants of the germinal spot gradually vanish, and he 

 maintains that the spindle is formed at the expense of the germinal spot. 

 The stage with this spindle corresponds with fig. 25. 



Several of Hertwig's figures closely correspond with those of Fol, and 

 considering how conflicting is the evidence before us, it seems necessary 



FlG. 25. OVUM OF ASTERIAS GLA- 

 CIALIS, AT THE SAME STAGE AS FIG. 24, 

 TREATED WITH PICRIC ACID (copied 



from Fol). 



