THE OVUM IN THE AMPHIBIA. 177 



able to distinguish any separate nucleus, or germinal spot, which seems, at this time, 

 to have disappeared as a distinct body. The germinal vesicle thus near its matuiity 

 is a mother-cell that contains a multitude of daughter or secondary cells, each, appa- 

 rently, including its own progeny. 



It is thus certain that the germinal vesicle exists in the ovum of the Frog until after 

 the period of hybernation. But in individuals that have been several days abroad, and 

 in which the ova are so far matured as greatly to distend the body, and be nearly 

 ready to leave the ovisacs, I have not always been able to detect the vesicle. The 

 yelk has then a greater proportion of white substance in its interior, intermingled with 

 the dark, and this, I suspect, is the result of the disappearance of the vesicle. 



In the ovum of the Toad, when as nearly mature as that of the Frog before leaving 

 the ovisacs, I have been unable to detect any trace of the germinal vesicle. The 

 dark portion of the yelk is then quite distinct from the light, and forms a cortical 

 stratum of intensely black pigment, scarcely more than one-sixth of the diameter of 

 the yelk in thickness. The light portion is of a yellowish white, and from which the 

 germinal vesicle, when present, is not readily distinguished. But at a little earlier 

 period, although only a few days before the pairing of the Toad, I have found the 

 vesicle fully as large and as distinct as before its disappearance in the egg of the 

 Frog, but situated more distant from the centre, and nearer to the black, the future 

 dorsal surface of the egg. 



In the great Water Newt, Triton palustris, the yelk of the matured ovarian ovum is of 

 a dull pea-green colour, which in spirit is changed to a greenish yellow. On breaking 

 open the yelk of this species, after it has been hardened in spirit, I have always found 

 the germinal vesicle of the same opake, intense white colour, of precisely the same 

 structure, and situated in the same part of the yelk as in the Frog. It has also a 

 canal passing from the middle of the surface of the darker-coloured portion of the 

 yelk, through its substance to the vesicle, as in the Frog. 



In the lesser Newts, Lissotriton punctatus and L. palmipes, the yelk is of a brown 

 or liver colour on the future dorsal surface, with a white central spot, and of a white 

 or pale straw colour on the ventral. In ripe ovarian ova of these species also I have 

 found the germinal vesicle of the same white colour, and having the same structure 

 as in the larger Triton and the Frog. 



In each of these instances, not merely when the ovum is immature, but even when 

 nearly ready to leave the ovisac, the germinal vesicle is situated in the interior of the 

 yelk (fig. 6), and not immediately at the surface, and thus far the fact is in accord- 

 ance with the observation of Dr. BARRY, that in the Mammalia the germinal vesicle 

 is in the interior of the ovarian ovum, and does not disappear on the surface. But, 

 nevertheless, it is not in the centre of the yelk, its place, as I have stated, is excentric. 



Time of disappearance of the Vesicle. It is well known that in frogs and toads 

 the ovum is never impregnated until after it has left the body, and consequently not 

 until long after it has left the ovary, and the germinal vesicle has entirely disappeared. 



MDCCCLI. 2 A 



