290 JORDAN. [Vol. VIII. 



the only observation I have made that would tend to such an 

 inference, and cannot in itself be regarded as convincing. 



The yolk-nucleus in the egg of the newt, then, arises from the 

 cytoplasm, and usually disintegrates in the cytoplasm. It is 

 likely, however, as I have already intimated, that yolk-nuclei 

 are sometimes fused with the germinal vesicle. I am 

 strongly inclined to believe that such fusion actually occurs, 

 although I am unable to produce any very conclusive evidence 

 in favor of such a belief. The fact that a considerable num- 

 ber of yolk-nuclei in late stages of the ^gg are sunk in a 

 hollow of the vesicle, and in some cases almost surrounded by 

 its substance, gives strong ground for such an opinion. In 

 Fig. 16, PI. XVI, is shown a yolk-nucleus apparently coalesc- 

 ing with the germinal vesicle. The union in this instance is 

 less pronounced than is sometimes the case, and I have fre- 

 quently obtained preparations which show the yolk-nucleus 

 engulfed to half its extent. 



Not uncommonly the yolk-nucleus in these later stages ap- 

 pears to be split up into irregular polygonal fragments (Fig. 13), 

 but as this does not appear to be invariable no great signifi- 

 cance can be attached to it. It is very likely a mere sign of 

 approaching dissolution. 



It is evident, I think, if we compare the observations above 

 recorded with those upon the structure and history of the 

 " yolk-nuclei " in other groups of animals, that if all the obser- 

 vations of different authors are to be credited, any real homology 

 between these bodies is out of the question. It is incredible that 

 bodies so widely diverse in origin, structure and fate as the 

 "yolk-nuclei" of Arachnids, Myriopods, and Amphibia should 

 be homologous in any ordinary sense of the word. The only 

 respect in which some of these bodies resemble one another 

 is in appearing in the cytoplasm at some stage in the develop- 

 ment of the ovarian ovum. It seems to be true, furthermore, 

 that the yolk-nucleus is not of general occurrence in all species 

 of the same group of animals. Although it is present in many 

 amphibian eggs, according to Gotte ('75) it is altogether absent 

 in the ovarian eggs of Biifo and Bombinator. Indeed, it is said 

 that yolk-nuclei are not always found in all the eggs of the 



