DE. W. H. EANSOM ON THE OVUM OF OSSEOUS FISHES. 
443 
that of the objects to be examined, for good definition. The germinal vesicle 
appears to be filled with a homogeneous and colourless colloid material. It is true, 
however, that a finely molecular structure in it might in this way escape notice. The 
germinal spots are imbedded in this colloid matrix, on its surface only, so as to be 
in contact with the inner surface of the wall of the vesicle ; unless, as often happens 
from mechanical causes and from imbibition, they have been displaced. They have a 
round form, homogeneous aspect, and a refractive power but little greater than that of 
the yelk-fluid (Plate XV. fig. 16). 
A more convenient mode of seeing the natural condition of the germinal spots, is to 
use a very minute quantity of water in cutting up the fragment, and to examine rapidly 
before time is allowed for changes to take place. Then, the spots are seen round and 
homogeneous-looking, when within their vesicles in larger ova, water not having reached 
them by imbibition. But in the vesicles of the smallest eggs, or in those which lie 
free in the field, the spots when first seen are variously tailed and vacuolate, parietally 
placed in the vesicle, lenticular when seen edgeways, their outlines much darker, and 
harder, perhaps, in part, an effect of contrast. The colloid matrix is usually seen deli- 
cately shaded by a fine molecular deposit, but the conditions of the formation of this 
molecular deposit I could not feel quite sure of, except that water favours it. 
More abundant and prolonged action of water is apt to displace the germinal spots, by 
distending the vesicle, but this it does irregularly, so as to make it appear in some measure a 
result of mechanical injury (Plate XV. fig. 17). The colloid matrix, after a time, becomes 
more granular, and this change may even obscure the germinal spots, when a weak solu- 
tion of chloride of sodium dissolves the fine granules, without impairing the consistence 
of the colloid matrix. This was well seen in one instance, at a rupture in the wall of a 
large escaped vesicle, in which also the extreme toughness and strength of the vesicular 
wall was manifest. The action of water, however, on the spots and on the colloid matrix 
is not the same on free uninjured vesicles, as it is on those still within the egg, especially 
the larger ones ; in which I found that the results were in great measure due to the 
influence exerted by the saline or other constituents of the yelk, which were carried into 
the vesicle by osmose. Thus, in larger eggs of group 3 and smaller ones of group 2, 
when long acted on by water, the germinal spots of contained vesicles are seen to get 
pale and disappear ; at the same time the ovisac and yelk-sac show evidences of 
abundant endosmose, and there is also some granular deposit in the cortical layer of the 
yelk, but not such as will account for the obscuration of the spots, as the position of the 
germinal vesicle is well seen, marked by a clear area (Plate XV. figs. 13 & 14). Still 
later on, the contents of the germinal vesicle are seen as distinct granules in rapid tremor. 
These facts strongly suggest the notion that the germinal spots are soluble in some of 
the constituents of the yelk, and we may thus explain their disappearance in ripe ova. 
It should be here mentioned that free germinal vesicles, being uninjured, remain in 
water for hours, without much visible distention or displacement of their contents, or dis- 
appearance of the germinal spots ; and the same may be said of those contained in very 
