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Part III, — Sixteenth Annual Report 



0-008mm. They are globular, and appear to consist of a thin 

 shell full of numerous spherical granules or vesicles, or both. The larger 

 spheres, from their pale unstained appearance and their size, seem to be 

 vesicular ; the largest of these measures almost, but not quite, 0"007mm. ; 

 the smaller correspond closely in size and appearance to the free 

 spherical granules or vesicles in the meshwork. One of the nucleoli 

 contains no granules or vesicles, and seems to consist merely of the 

 shell, which is somewhat crumpled. The conclusion seems warranted 

 that the free granules are derived from the breaking down of the nucleoli. 

 Other sections of this germinal vesicle show the same thing, as well as 

 sections of the germinal vesicles in other eggs in the same ovary, less 

 excentrically placed, the nucleoli in these being all aggregated at one side. 



In one or two cases only was I able to detect the chromosomes in 

 these eggs. Fig. 7, Plate III., represents the edge of a germinal vesicle, 

 showing four nucleoli in process of disintegration, and between two of 

 them the chromosomes were distinctly visible. 



The conclusions to which I have arrived with regard to the changes at 

 maturation in the eggs of teleostean fishes may be summarised as 

 follows : — 



(1) In both pelagic and demersal eggs the final stage at the 

 close of ovarian growth is characterised by the entrance into the 

 ovum of a certain quantity of watery fluid of low specific gravity. 

 This fluid is secreted by the granular cells of the follicle, and is 

 probably essentially similar in composition to the free fluid found 

 in ripe ovaries producing pelagic eggs. 



(2) This fluid causes the more or less complete fusion or solution 

 of the yolk-spherules, and hence the translucency or transparency 

 of the vitellus ; and it is associated with the dissolution of the 

 germinal vesicle and the rearrangement of the chromatic substance 

 concerned in fertilisation and heredity ; also with the escape of 

 the egg from the follicle. 



(3) In pelagic eggs which float isolated in the sea, the quantity 

 of fluid that enters the ovum is very large, distending it to three 

 or four times its former volume, and completely dissolving the 

 yolk-spherules ; and that such eggs float by virtue of the large 

 quantity of fluid of low specific gravity absorbed. 



(4) That in one form at least (Lophius piscatoHus), and 

 probably in others, this change is preceded or accompanied by a 

 change in the constituents of the germinal vesicle, the nucleoli 

 travelling towards the centre of the latter, and breaking up into 

 minute stained granules, which may possibly take part in the 

 formation of chromosomes. The hydrolytic change may be due 

 to decadence of the histogenetic function of the nucleoli, the 

 components of which then break up as described. 



To these I may add 



(5) That inasmuch as the entrance of fluid in demersal eggs has 

 no hydrostatic function, and is of no utility in connection with 

 the external relationship of the ovum, the same change is probably 

 of normal occurrence in the maturation of the ovum in other 

 groups of vertebrates, and in some groups of invertebrates.! 



t Fol, in his early observations on the transformation of the germinal vesicle of 

 Asterias glacialis, states that the change does not occur until the egg has reached the sea 

 water. It is not improbable that in some forms there may be direct absorption of sea 

 water instead of follicular secretion. 



