OVARIRS IN TPILEOSTEAN AND ELASMOBRANCH FISHES. 169 



perceutage of nucleic acid they stain witli methyl green, 

 the crucial test for chromatin. Methyl green is a notoriously 

 difficult reagent to work with, and I was not successful in 

 getting the nucleoli of teleostean ova to stain with it. With 

 safranin, however^ which is usually cited as a typical basic or 

 chromatin dye, one can get the nucleoli to stain deeply or 

 even exclusively if the washing-out process has gone far 

 enough. The fact that the same nucleoli which show so 

 decided a basophile or acid reaction when treated with 

 methyl green or safranin are equally or even more prone 

 to stain with eosin, a dye which is supposed to have quite 

 opposite affinities, is not very easy to understand. The red 

 blood-corpuscles are regarded as pre-eminently eosinophilous 

 or acidophilous bodies. If, then, the reaction to eosin of 

 these bodies can be used as a standard of comparison, then 

 it is clear that the nucleoli of the germinal vesicle arc 

 sti'ongly acidophilous, i.e. basic structures containing a high 

 percentage of albumen or low percentage of phosphorus. 

 We are thus led to contradictory i^esults. One conclusion 

 to be drawn from all this is that it is not always safe to 

 make deductions in regard to the chemical nature of the 

 various structures of the cell from a study of differentially 

 stained sections of material which has been fixed in the 

 ordinary liquids. If, on the other hand, we may rely on 

 Mann's methyl blue-eosin method, the staining reactions 

 certainly point to this. The microsomes of the germinal 

 vesicle as they grow and become transformed into karj'O- 

 somes or nucleoli undergo a chemical change, losing phos- 

 phorus or acquiring a larger proportion of albumen. Thus 

 the change from blue to red is accounted for. 



1. Post-embryonic Origin of Ova and Follicular 

 Epithelium. 



In foetuses of Zoarces 30 mm. long all the sex cells in the 

 ovary were equal in size, and in a state of active karyokinetic 



