278 MR. F. E. BEDDARD ON THE [May 4, 



In older ova the germinal vesicle has altered somewhat from the 

 characters which it presents in the earlier stages of the matu- 

 ration of the ovum. In Plate XXIX. fig. 1, I have sketched a 

 germinal vesicle precisely as it appeared in transverse section. It 

 will be noticed, in the first place, that the germinal vesicle is very 

 sharply marked off from the surrounding substance of the ovum, 

 and in the section figured has become separated from it throughout 

 a considerable area ; this separation is no doubt due to shrinkage, 

 but serves to show the very trenchant line of division which separates 

 germinal vesicle and ovum, since no yolk-spherules were found to 

 remain adherent to the germinal vesicle. 



The substance of the germinal vesicle in ova of this stage of develop- 

 ment has become specialized into an outer peripheral portion and a 

 central core. These two areas of the germinal vesicle are almost as 

 sharply marked off from each other as is the outer layer of the ger- 

 minal vesicle from the surrounding egg-protoplasm and yolk. This is 

 clearly shown in the same figure (Plate XXIX. fig. 1), and, as in the 

 first case, is probably due to shrinking of the germinal vesicle when 

 plunged into the preservative reagent. Along the upper side of the 

 preparation illustrated in the figure already referred to, the central 

 core of the germinal vesicle has shrunk away from the external 

 sheath ; along the lower margin of the germinal vesicle the con- 

 traction has not caused a separation of the two constituents, but a 

 split in the outer layer, which I have not indicated in the figure. 



The outer coat of the germinal vesicle is very easily distinguish- 

 able from the inner core ; it is much more finely granular in 

 structure, appearing occasionally almost homogeneous, and has 

 become stained a pale pink. The inner core is more coarsely 

 granular, and has a yellowish tinge, hardly owing to the non- 

 penetration of the staining reagent, since the imbedded nucleoli 

 were deeply stained. 



The substance of the internal core contained elliptical spaces here 

 and there, which are possibly themselves due to contraction. The 

 boundary line between the central core and the peripheral layer is 

 also marked by the nucleoli, which are for the most part situated in 

 a single layer at the extreme periphery of the central core. A few, 

 however, as indicated in the figure, are to be found in the more 

 central regions of the core. The nucleoli were extremely conspicuous 

 owing to their vivid staining with the reagent, and appeared to be 

 solid, being uniformly stained throughout. In the earlier stages of 

 the germinal vesicle mention has already been made of the annular 

 appearance of the germinal spots. The germinal spots were very 

 unevenly distributed and of varying size, but were never found in 

 the peripheral layer of the germinal vesicle. 



In Triton, Iwakawa has described what appear to be very 

 similar changes in the germinal vesicle, though there is some little 

 difference in detail ; as the egg approaches maturity the germinal 

 spots move in towards the centre of the germinal vesicle, leaving a 

 homogeneous, more deeply stained peripheral area. 



