442 
DR. W. H. RANSOM ON THE OVUM OE OSSEOUS EISHES. 
vesicle is neither food-yelk nor formative yelk, but differs in structure and reactions 
from both in a very marked manner, although it contains probably a little albumen b *. 
It may be called primitive yelk. That water and other fluids cause no visible vacuola- 
tion in its substance may possibly be due to the fact, that if it were delicate it might be 
obscured by the changes which are produced at the same time in the cells of the ovisac, 
and which at times are very confusiug. 
The primitive yelk is very firm, and often escapes on cutting up a fragment of an 
ovary in 1 per cent, solution of chloride of sodium, or in a solution of glycerine 2 per 
cent., as a solid-looking, somewhat angular body, with its contained germinal vesicle 
(Plate XV. fig. 15). In water also it is solid, though much paler, when escaped, than in 
the other media. Although it is not like the perfect formative yelk in structure or pro- 
perties, it may possibly be continued in a modified form, and exist in some proportion 
in the ripe ovum, as its reactions are rather negative than positive, and it might there- 
fore easily escape detection. 
To the primitive yelk, as the eggs grow, are added the other elements ; first, of the 
formative yelk, and afterwards of the food-yelk, as the above-mentioned reactions prove. 
The precise time of the appearance of the food-yelk was not made out with certainty ; 
it is probably some time before the oil-drops make their appearance, and possibly the 
clear halo around the germinal vesicle is the first optical expression of it. What its 
precise relation to the germinal vesicle and formative yelk may be at first, I could not 
determine. The solidity of the primitive yelk reminds one forcibly of the early condi- 
tion of the yelk in the ovum of Birds. 
Whether any inner sac exists in ova of the groups 3 and 2, I cannot say. I could 
only find it in group 1, i. e. nearly ripe ova; and one observation seemed to indicate that 
in group 3, at least, it is not present ; for these eggs, when examined in saliva, show the 
yelk-sac distended, together with the ovisac as one membrane, and then the surface of 
the yelk is granular and irregular, not smoothly defined as it would be, were an inner 
sac present. 
At no time did I observe any contractions of the protoplasm of immature ova : perhaps 
I did not use the requisite media ; but the solid state in which it exists at first makes 
it difficult to conceive how such could occur. 
The germinal vesicle and its contents also require that various reagents, of different 
degrees of concentration, shall be employed in their examination. 
The first difficulty is to get to understand the natural aspect of such variable objects, 
and to appreciate duly the influence of the media used. 
By cutting up a large piece of an ovary without any fluid, and selecting a small frag- 
ment for examination, the smaller eggs and the germinal vesicles may be studied, and the 
latter seen both in ovo, and free in the field ; but the field is turbid, and the refractive 
index of the medium, which is a mixture of escaped yelk and serum, is too much like 
* See page 451 for a description of this variety of albumen, which is probably a constant constituent of the 
yelk of vertebrata. 
