[5] EMBRYOGRAPHY OF OSSEOUS FISHES. 459 



or i)osition occurs. When the eggs are one-half or nearly fall grown, 

 the protoplasm surrounding the germinative vesicle becomes uniformly 

 corpuscular, and, hence, diflerent in character from that found in quite 

 young eggs. Such partly developed ova, when examined with reflected 

 light, appear whitish instead of a clear, transparent, yellowish tint, 

 such as would be noticed in ripe eggs. This difference in color is due 

 to a change in the character of the plasma enveloping the germinative 

 vesicle, for immediately that the eggs are mature and ready to leave 

 the intraovariau cavity they acquire a remarkable transparency. This 

 must be due to a comparatively sudden blending of the protoplasmic 

 corpuscles of the egg into a homogeneous material, very like the white 

 or colorless albumen of a hen's egg, but differs from the latter again in 

 that it becomes whitish, — coagulates when brought into direct contact 

 with water. It would be a matter of great interest to know the chemi- 

 cal composition of the yelks of the ova of a large number of genera. 

 Equally important it is to know what particular x>roteids enter into 

 their composition besides the oils and coloring matters characteristic of 

 certain species. The yelk material of the cod's egg in its change from 

 the younger granular state is, however, not perfectly homogeneous, any 

 more than that of the shad. Here, as in that species, it is made up of very 

 minute corpuscles, which are themselves very transparent and involved 

 in a clear i)lasma. I have never isolated the flat, somewhat crystalloi- 

 dal bodies which have been observed in the eggs of Cyprinoids. This 

 proteid has been named ichthyine by Valenciennes and Fremy. Such 

 ovoidal bodies constitute almost the entire bulk of the ova of the Amer- 

 ican Cycloganoid, Amia calva, as I have had the opportunity to learn 

 from an examination of a fresh, nearly mature ovary of this fish in Xew 

 York in February, 1882. It is not a little remarkable that, amidst 

 all the diversity of color and size of the ova of Teleosteau fishes, we 

 should also find differences in the microscopic character of the yelk of 

 the different species ; a fact which ought, once for all, to be sufficient to 

 silence a mischievous class of compilers who insist upon asserting that 

 the germs of different species of animals are so nearly alike as to be 

 indistinguishable from one another. The office of the yelk is to supply 

 nutrient matter to the embryo Avhich is superimjjosed upon it, and tlie 

 membranes of which completely inclose it. We may in ripe ova distin- 

 guish, first, yelk corpuscles, these again sometimes aggregated into large 

 granular bodies, which may themselves be involved in a meshwork 

 continuous with the cortical layer from which the germ disk is derived. 

 Finallj", oil drops may be present in many other forms, such as Hip- 

 pocampus, Siphostoma, Cyhium, Parephippns, and all Salmonoids which 

 I have ever observed, to which we may add Cyprinodonts and some 

 Percoids. Exceptions in regard to structure occur, however, even 

 within the bmits of families ; for example, the cod's egg is without any 

 oil drop, while in another Gadoid, Brosmius americanus, the eggs con- 

 tain a large pinkish oil drop, placed eccentrically, like that of the Spauisla 



