DR. W. H. RANSOM ON THE OVUM OF OSSEOUS FISHES. 
441 
to see in eggs of about ttto^ a clear halo around the germinal vesicle, bounded by a 
defined, but irregular granular outline. At present I hesitate to express any decided 
opinion as to whether this indicates a first separation of the yelk into two kinds. 
A solution of chloride of sodium of 2 per cent, contracts or shrivels the tissue of the 
ovary, and makes the eggs, when they are above the very smallest size, opaque, by pre- 
cipitating in them the matter of the cortex. 
Solutions of acetate of potash of 5 per cent, or 2 per cent, cause the egg, with its 
yelk-sac, to shrink within the ovisac, which dilates ; make the larger eggs of the third 
group opaque by precipitating the formative yelk, and leave the smallest homogeneous 
eggs clear, do not permit the clear halo to be seen, and make the yelk-sac paler. 
Solution of glycerine, per cent, is a very good medium, it leaves the field clear, 
all the objects well defined, but shrivels the egg a little in the ovisac. 
Strong glycerine is quite unsuitable, it changes the appearance and form of the yelk- 
mass, and obscures the germinal vesicle at times completely ; nor can the natural appear- 
ances be restored to specimens preserved in it by adding water. The ovarian stroma is 
also obscured in it. 
The yelk requires to be examined in various media in order to make out its structural 
elements, and its separation into food and formative yelk. 
Water, although in using it great care is required, on account of the rapidity with 
which it changes everything, is very useful. When used abundantly it causes a fine 
granular precipitate in the substance of the yelk, in the very smallest ova met with, due 
probably to the presence of albumen b, but does not cause visible vacuolation in the 
yelk. It also permits, in the larger eggs of group 3, and the smaller of group 2, the 
clear halo around the germinal vesicle to be seen ; at the same time it causes a granular 
deposit in the cortical layer, and then gives rise to vacuolation ; and if the eggs are at 
that stage that yellow droplets have appeared, they grow pale and disappear. 
A 1 per cent, solution of acetate of potash slowly causes a precipitate in the cortex 
of eggs above the very smallest ; very slightly also a turbidity of the smallest egg. 
A solution of 1^ per cent, of chloride of sodium, which does not alter the blood-disks 
of the same fish, also causes a dark precipitate in the cortex of eggs which have a 
distinction of yelks. 
A 1 per cent, solution of glycerine is the most neutral agent, as far as regards the 
yelk-substance, but after some time the yelk of all ages becomes slightly granular in it. 
In trying to determine at what stage of development the granular elements of the 
cortical layer appeared, it was necessary first to find a fluid medium which did not de- 
termine a precipitate. The maternal fluids may be used, but do not enable one to ob- 
tain a clear field. 
5 and per cent, solutions of acetate of potash precipitate the larger of these eggs 
strongly, the smaller less so, the smallest not at all, and their yelks escape in a solid 
form. The yellow droplets change very slowly in these solutions. 
Hence it is safe to say, that the substance which is first seen around the germinal 
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