OVARY AND OVAEIAN OVA IN CERTAIN MARINE FISHES. 148 



somes without a nucleolus are not the same as chromosomes 

 plus a nucleolus. It is not probable that the nucleoli are formed 

 from the achromatic elements; on the contrary, there is much 

 evidence indicating their connection with the chromatin. 



If the chromosomes are of great physiological importance, 

 it must be because they influence the life of the cell, they 

 must take part in the general metabolism of the cell. If they 

 were merely fixed elements which were divided and trans- 

 mitted in permanent form from generation to generation of 

 cells, it would be difficult to understand how they could affect 

 the properties and qualities of the cell. To say that the chro- 

 matin is the substance of heredity, merely means that judging 

 from the history of the spermatozoon in fertilisation, all the 

 peculiar qualities which are transmitted from parent to off- 

 spring must be contained in the chromosomes of the pro- 

 nucleus. Even this is not strictly true, because there are the 

 centrosomes to be taken into account. But the number and 

 form of the chromosomes are nothing unless we know how 

 they act upon the cell and determine its behaviour. 



The small ovum in fig. 21, PI. 3, shows the appearance of the 

 germinal vesicle in ova of the flounder of '037 mm. diameter. 

 The reticulum is but slightly stained, more by haematoxylin than 

 by safranin, the large nucleolus is deeply stained, and the cyto- 

 plasm also takes stains very deeply at this stage. In this respect 

 the cytoplasm of the ovum at this stage differs from that of 

 other cells, and from that of the ovum at other stages. The 

 cytoplasm is very dense and almost homogeneous in appearance. 

 The other ovum represented in fig. 21 is "098 mm. in dia- 

 meter. The germinal vesicle in it is much larger than in the 

 smaller egg, there are several small nucleoli in contact with 

 the membrane of the vesicle, and there is a nuclear network, 

 some strands of which are more stained and more conspicuous 

 than the rest. The cytoplasm is granular, and after the 

 action of chromic and osmic acids scarcely stained, but in 

 material fixed with picro-sulphuric or sublimate it stains con- 

 siderably. In the stage here considered there is a distinct 

 membrane. 



