476 REPORT ON ZOOLOGY, MDCCCXL1V. 



other ova which existed in great abundance, however, 

 possessed an external elliptic egg-membrane which was of 

 tolerable thickness, more or less distant from the vitelline 

 membrane, from which it was separated by a clear fluid 

 without granules. The germinal vesicle was recognised in 

 only some of these ova ; there was always a vitellus very rich 

 in granules. Other ova again, of a larger size and more 

 elliptic form, consisted of an external egg-membrane, and of 

 a vitelliue membrane closely applied to it, which was en- 

 tirely filled with granular vitelline substance. In ova of a 

 still larger size Kolliker observed in the centre of the vitellus 

 a clear spot, the size and transparency of which continued 

 to increase, and which finally broke through the vitellus ; 

 during the increase of this clear spot the vitellus gradually 

 diminished, until at last it disappeared entirely, and the 

 clear spot, which consisted of an assemblage of self-multi- 

 plying embryonic cells, occupied the whole of the vitelline 

 membrane. Hereupon the embryonic cells were divided 

 into a peripheric and a central layer, the latter at first 

 appeared roundish, soon became pyriform, and rather flat- 

 tened, and was finally transformed into the true embryo, on 

 which, on more particular inspection, the six booklets 

 arranged in pairs could be recognised. Kolliker supposes 

 that this embryo grows at the expense of the peripheric 

 layer, and ultimately breaks through the egg-membrane. 

 Since, moreover, on no single occasion did he find the ova 

 containing a living embryo, as large as those ova in which 

 the germinal vesicle had disappeared, and since these again 

 were larger than those which did not yet possess a choriou, 

 he assumed that in the first stages the vitellus is still 

 increasing in bulk, and mechanically distends the egg- 

 membrane, but on the appearance of the embryonic cells, 

 the latter enlarge at the expense of the vitellus. 



Kolliker (Miiller's Archiv, 1843, p. 99) has found m 

 abscess-like cavities of the liver of several Rabbits a yellow, 

 puriform, thickish matter, consisting of ova, which were in 

 various stages of development, analogous to those of the 



