DE. W. II. EANSOM ON THE OVUM OF OSSEOUS FISHES. 
467 
reminding one of the “ Faltenkranz ” described by Eeiciieet *, and M. ScHULTZEf, in 
the frog’s egg (Plate XVII. figs. 55 Sc 56). 
The cleavage masses at no time can be seen to contain any nucleus, vesicular or solid, 
nor could I find any in the germinal disk prior to cleavage. After twenty hours the 
germinal mass consists of a cup-shaped group of cell-like corpuscles, the result of re- 
peated segmentation, seated upon the germinal pole of the yelk (Plate XVII. fig. 57), 
without any differentiation of parts. It is closely connected with the inner sac, which 
may be seen at its outer boundary forming radially arranged folds. The mass is solid, 
and its elements cohere with some tenacity, but on rupture in water the cell-like cor- 
puscles in part separate, and as they float away undergo vacuolation. 
The surface of contact of the germinal mass with the food-yelk is difficult to study. 
It seems to be merely the corpuscles resulting from segmentation in contact with the 
fluid food-yelk. 
It is not without interest to note, in passing, how frequently, from slight causes, 
among which pressure seems to be the most important, an asymmetrical cleavage occurs ; 
and the possibility of artificially inducing the formation of monsters is thus suggested 
(Plate XVII. figs. 56 & 58). One egg, in which the irregular cleavage had been seen, 
showed on the eighth day a well developing embryo, about to burst the yelk-sac, but no 
visible deformity. 
3. Conditions of the Yelk Contractions and of Cleavage. 
a. Poisons . — Experiments were made on impregnated ova of the two species of Cas- 
ter osteus, to ascertain how far the contractions of the yelk, and the cleavage were influ- 
enced by poisonous substances. 
Hydrocyanic acid , when very dilute, produced no visible effect upon the rhythmic 
contractions of the yelk, but caused a little delay in the commencement of cleavage. 
When used a little stronger it slowly produced rupture of the inner sac, without pre- 
viously seeming to influence the rhythmic movements; and it delayed still more the 
cleavage in those eggs which had not ruptured the inner sac. When used still stronger 
it arrested the rhythmic contractions, but at the same moment caused bursting of the 
inner sac and opacity of the yelk. 
Atropia . — A supersaturated aqueous solution had no apparent effect on the yelk con- 
tractions or on cleavage. 
Aconite . — The spirituous extract, mixed with water, did not influence the yelk con- 
tractions, but retarded the cleavage. The next day the yelks had undergone chemical 
change. 
Strychnia . — The aqueous solution had no apparent effect. 
b. Galvanism . — The following observations were made to ascertain the influence 
exerted by the galvanic current upon the yelk contractions, and on cleavage. In my 
* Archiv fur Anatomie, Physiolog'ie, Ac., 1861 and 1863. 
f Olbservationes Nonnullas de Ovorum Eanarum Segmentatione, 1863. 
