438 
DR. W. H. RANSOM ON THE OVUM OF OSSEOUS FISHES. 
When an egg is ruptured by pressure in water, and the germinal vesicle is seen as it 
escapes, it shows the contents more changed, and it is very apt to vanish quickly in the 
water, as if from some injury received during its expulsion. However, sometimes it may 
be examined in this mode, if no time be lost, and then the germinal spots are very 
irregular. At a rough estimate the number of spots is about 100 at this period. They 
are slowly dissolved by a solution of sal-ammoniac, the molecular matrix more quickly 
so. Dilute acetic acid, added after the action of the sal-ammoniac, causes a copious, 
very fine dark granular precipitate within the vesicle. 
In one instance I found eggs measuring the average size of ripe free ova, which 
contained the germinal vesicle with contents precisely as above described. In this case 
the oil was more concentrated, the eggs clearer-looking to the naked eye ; and as a 
further proof of their being nearly ripe, the oviduct was furnished with a store of the 
viscid material ready to cover the ova as they burst the ovisacs. Not all the eggs, how- 
ever, of the same batch have exactly the same dimensions, and still less have those of 
different individual parents when ripe and free. In one, at least, of these ovarian ova 
I ascertained that the germinal vesicle had disappeared. 
In the nearly ripe ovarian ova, from about ys " to -£ 5 ", in which the germinal vesicle 
is visible, there is a cortical layer of formative yelk, a thicker layer of it, or discus 
proligerus, at the germinal pole, essentially identical in structure and properties with 
the same parts in the deposited eggs. There are some slight differences however, the 
most distinctive being, that larger droplets, apparently identical with the matter forming 
the yellow droplets, but a little paler in colour, occupy a deeper plane in the cortex, 
chiefly of the germinal segment. These undergo similar changes of vacuolation, and 
have identical reactions with the yellow droplets. This vacuolation presented at the 
same time in various parts of the escaped formative yelk both lilac-tinted and colour- 
less vacuoles, shown, by their inverting an image seen through them when beyond focus, 
to have less refractive power than the surrounding medium, and by their gradual growth 
and fusion, to be in reality drops of a limpid fluid. Between these limpid drops there 
appeared various kinds of granules and semisolid-looking refractive, yellow, crescent- 
shaped masses, partly or wholly surrounding the vacuoles, thus giving rise to appear- 
ances like young cells. Sometimes a number of minute vacuoles formed within a large 
homogeneous-looking yellow droplet, and thus a pseudo-granular corpuscle resulted. 
But all these appearances were fleeting, and the variations infinite, depending in some 
degree on the nature of the medium which had been used. Thus water caused the 
vacuolation most rapidly ; the viscid secretion of the oviduct and the food-yelk, I have 
before said, excite it, although slowly ; the same may be said of the scanty succus, or the 
blood or serum contained in the tissues of the ovary, or of weak solutions of glycerine 
or sal-ammoniac ; this latter, by causing a precipitate in the matter of the formative yelk, 
complicates still further the forms which result from these changes. There is seen at 
the under surface of the discus proligerus, and forming a part of it, the little heap of fine 
dark oil-granules, distinct from the store of oil which floats in the food-yelk. The inner 
sac is distinctly to be made out in these ova. 
