DR. W. H. RANSOM ON THE OVUM OF OSSEOTJS FISHES. 
449 
be conceived to grow by apposition of layers added from the inside or outside, although 
its laminated structure might at first be supposed to afford some support to this view ; 
for the increase in number, as the growth proceeds, of the buttons placed on the outer 
surface, and their early appearance, make it impossible to understand growth by either of 
these modes. It is, I think, certain that it grows interstitially, and the suggestion arises 
that the larger stellar dots may in some way be connected with this increase. 
The fact that young ovarian ova, of yjfo" in diameter, when the dots are first measured 
show them to average about 24,000 to an inch linear, and ripe eggs five or six times 
their diameter have 11,000 dots to an inch, thus but little more than doubling their size 
or distance apart, proves that during growth the number of these structural elements 
of the yelk-sac must increase, as well as their size. This may be taken as an additional 
proof of interstitial growth. 
There is no evidence of the conversion of the substance of the outer layer of the pro- 
toplasm, i. e. the cortex of the yelk, into yelk-sac, in the sense in which that gradual 
conversion is believed by Dr. Beale to take place in cartilage ; at least after arrival 
at that stage, and it is a very early one, at which the yelk-sac is separable : as then it 
always shows its inner and outer surfaces equally sharp, hard, and distinct. 
There are no facts known to me to point out whether the pabulum for the growth of 
this membrane is derived directly from the currents passing inwards, or from the mate- 
rial elaborated in the egg and passing out of it, or from both sources indifferently. 
The extreme delicacy of the film which covers the yelk at first, makes it impossible to 
say positively whether it appertains rather to the layer of cells lining the ovisac, or 
whether it is more closely adherent to the yelk ; but 1 incline to the latter view. 
The germinal vesicle , which, both from the facts here recorded, and from the analogy 
of the eggs of invertebrata, appears to be formed before the primitive yelk, may be 
supposed, from its disappearing when the egg is ripe, before fecundation, or the action 
of external agents, to preside over the origin and growth of the egg. However, the 
position in which it is last seen with respect to the micropyle, as strongly indicates that 
its remnants have some important relation to. the act of fecundation. 
Balbiani* has recently, in a paper which received a prize from the French Academy, 
stated that the germ (with him the equivalent of the formative yelk) may be traced to a 
preexisting nucleated cell spontaneously arising on the surface of the food-yelk, which 
cell by endogenous development of cells at the expense of the “ primordial protoplasm ” 
(food-yelk) forms the future germ on its surface. He expressly extends this view to 
osseous fishes, although he repeats the error made by Coste, that the germ (formative 
yelk) only appears after fecundation. 
This description of the mode of origin and growth of the parts of the ovum, I feel 
justified in stating is not in accordance with observed facts. 
* “ Sur la Constitution du Germe dans l’ceuf animal avant la fecondation,” Comptes Rendus, 1864, t. lviii. 
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