454 
DE. W. H. EANSOM ON THE OVUM OF OSSEOUS FISHES. 
water be present they imbibe it rapidly, and then become so adhesive, that every 
attempt to roll them and examine the surface tears off the outer layer of the yelk-sac, 
or “ eikapsel.” Before water is added they have a convoluted surface, such as a lax 
membrane presents, which is marked by irregular impressions of the cells which line 
the ovisac. When water is added it rapidly distends and effaces the convolutions, but I 
could not see any regular hexagonal facets such as have been described. A beautifully 
regular fine dotting, however, is seen arranged so as to enclose lozenge-shaped spaces. 
Any attempt to move the egg while in its adhesive stage, exhibits the wonderful 
extensibility of the outer layer, the shreds of which are drawn out so as to appear 
homogeneous. This adhesiveness is lost, however, after twenty-four hours’ immersion 
in water. The fine dottings may be best examined by placing eggs which have been 
thus macerated, in a solution of chloride of sodium, and after cutting them in halves, 
washing the yelk-sac and its capsule in a 1 per cent, solution of chromate of potash, 
so as to preserve it free from adhesiveness, and to remove the coagulated albumen b. In 
this way the outer layer appears to be continuous with, and of similar structure to the 
yelk-sac proper, from which it can in no way be separated as a distinct membrane. It 
seems probable, that the outer layer serves to fix or anchor the spawn upon the weeds 
or other bodies on which the female deposits them. 
The micropyle is very similar to that seen in the pike. It is, however, not easy to 
find in water while the eggs are adhesive, but weak solutions of the alkaline chro- 
mates, or of chromic acid with chloride of sodium, destroy the adhesiveness of the outer 
layer, without otherwise changing the aspect of the egg, and thus it may be mani- 
pulated, and the micropyle easily found. 
The Perch (Perea fluviatilis). 
The eggs may be expressed from a ripe female, cohering, so as to form a long flat 
band, folded in zigzag. This band is a collapsed tube, a network of eggs with irregular 
meshes, altogether not unlike a netted bead purse. 
The unimpregnated egg rapidly absorbs water so as to distend the yelk-sac and its 
outer layer or “ eikapsel,” and to form a water-chamber, while the formative yelk con- 
centrates as in pike and salmon. The structure of the egg as a whole, is the same as 
in the ruffe, and the oil is in one large drop. 
The yelk-sac, under which term is included the outer layer or “ eikapsel” of Muller*', 
merits a very careful examination, but I must give only a brief description of such 
observations as I have been able to make upon it. 
Like the outer layer of the yelk-sac in the ruffe, that of the perch is probably an 
organ of adhesion, but in this case the eggs adhere to each other before extrusion from 
the parent fish, and are not adhesive after they are expelled. The time they lie in the 
oviduct, free from the ovisacs, and during which they are definitely arranged to form the 
tube, is very short, probably about twelve hours only, as I found a female at 10 p.m. 
* “ Ueber zahlreiche Poren -canale in der Eikapsel der Fische,” Mtoler’s, Archiv, 1854, p. 186. 
