MATURATION AND IMPREGNATION OF THE OVUM. 



117 



its membrane becomes gradually absorbed and its outline in- 

 dented and indistinct, and finally its contents become to a 

 certain extent confounded with the vitellus (Fig. 3). 



The germinal spot at the same time loses its clearness of out- 

 line and gradually disappears from view. 



At a slightly later stage in the place of the original germinal 

 vesicle there may be observed in the fresh ovum two clear 

 spaces (fig. 4), one ovoid and nearer the surface, and the second 



Fig. 4. — Ovum of Asterias glacialis, showing the clear spaces in the place 

 of the germinal vesicle. Fresh preparation (copied from Fol). 



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

 By treatment with reagents the first clear space is found to be 

 formed of a spindle with two terminal suns on the lower side of 

 which is a somewhat irregular body (Fig. 5). The second clear 

 space by the same treatment is shewn to contain a round body. 

 Fol concludes that the spindle is formed out of part of the 

 germinal vesicle and not of the germinal spot, while he sees in 

 the round body present in the lower of the two clear spaces the 

 metamorphosed germinal spot. He will not, however, assert 

 that no fragment of the germinal spot enters into the formation 

 of the spindle. It may be observed that Fol is here obliged to 

 fill up (so far at least as his present preliminary account enables 

 me to determine) a lacuna in his observations in a hypothetical 

 manner, and O. Hertwig's (13) most recent observations on the 

 ovum of the same or an allied species of Asterias tend to throw 

 some doubt upon Fol's interpretations. 





Tig. 5. — Ovum of Asterias glacialis, at the same sta^e as Fit', i, treated 

 with picric acid (copied from Fol). 



