HE. W. H. EANSOM ON THE OVUM OF OSSEOUS FISHES. 
437 
b. Nearly ripe ova will be conveniently described here before the earlier ovarian ova ; 
and at the same time I shall attempt to trace the fate of the germinal vesicle and its 
contents. As the germinal spots have some resemblance to the yellow droplets of the 
formative yelk, and as both are so very unstable that they undergo visible changes in all 
ordinary media, a large number of observations had to be made with a view of deter- 
mining their characteristic reactions. 
Nearly ripe ovarian ova, having a diameter of to yg-", have the oil collected but 
imperfectly, and are not quite so yellow and clear-looking as ripe ova. The germinal 
vesicle can be seen in situ very well, by placing an egg without the previous contact of 
water on the slide, and using some pressure, the micropyle either presenting or in profile : 
the latter is the better mode. The vesicle is then constantly found excentrically placed 
in the egg, imbedded in the centre of the semi-solid discus proligerus, so that the apex 
of the micropyle comes nearly into contact with the centre of its surface directed to the 
germinal pole. At this period it appears lenticular when viewed in profile, and so closely 
connected with the substance of the discus proligerus, that on rupture of the egg by 
pressure, the vesicle carries with it, in escaping, a portion of the granular matter in which 
it lies. 
In an egg which measured the germinal vesicle had a diameter of ygy". Viewed 
with a power of X 50 the germinal spots are just visible, the other contents of the vesicle 
not at all, while it is in situ . To see the spots with higher powers, it is better to puncture 
the yelk-sac before applying pressure, so that the contents may escape with less violence. 
If an egg be ruptured by pressure in water, the germinal vesicle often escapes detection 
altogether ; but pressure short of rupture, without water, shows the vesicle very well, 
and if it be then increased so as to produce rupture, the vesicle may be easily traced as 
it passes from its natural position to the aperture in the yelk-sac, where, however, it 
often breaks and is lost. In all these modes the contents of the vesicle are apt to be 
displaced, and are so variable in aspect, that no doubt can remain of their being changed 
somewhat, either by the media they are examined in, or by mechanical violence. When 
by pressure and rupture without water the vesicle escaped without being destroyed, it 
was much distorted at the opening in the yelk-sac, but as it lay in the fluid of the egg it 
appeared round. Examined with a power of X 200 the germinal spots were numerous, 
loosely aggregated, rounded irregularly, of considerable refractive power, and without 
any distinct vacuolation in their substance, which had a homogeneous aspect and was 
almost solid looking (Plate XV. fig. 9). They measured on the average y^o"' Besides 
the germinal spots, the vesicle was nearly filled with a very delicate molecular matrix. 
When to this slide water was added, the vesicle imbibed it, and became distended at 
first unequally, the molecular matrix was displaced, the molecules seemed to darken 
(although this might be an effect of the greater contrast of refractive index merely^ , 
and among them delicate vacuoles appeared (Plate XV. figs. 10 & 11). The wall of 
the vesicle resisted the action of water and showed considerable tenacity, admitting of 
free manipulation. It was not dissolved by a solution of sal-ammoniac, or by weak 
acetic acid, which shrivelled it. 
