482 BULLETIN OF THE 



" Dotterplattchen " and fine pigment balls. He concludes that this veil 

 i3 really composed of remnants of the germinative vesicle, eliminated 

 from the yolk by the contraction of the protoplasm after the dissolution 

 and distribution of the substance of the vesicle, and of portions of the 

 3'olk substance. Rut there is no ground for a comparison of this with 

 the formation of polar globules. His own observations do not prove 

 whether this elimination may ensue without fecundation. On eggs 

 hardened about an hour after fecundation there may be observed, at one 

 side of the centre of the dark field, near the margin of the veil, a " pig- 

 mented process " extending obliquely into the yolk toward the middle 

 of the egg. The inner end of this projecting mass is swollen, and em- 

 braces a clear, finely granular substance which diff'ers from the rest of 

 the yolk. About this clear spot the pigment grains are radially ar- 

 ranged ; within it is a nuclear structure of much the same nature as the 

 pronuclei already described. This nucleus grows rapidly as the dark 

 process lengthens toward the axis of the egg, which it finally reaches 

 two thirds of the way from the surface to the centre of the yolk. Mean- 

 while a similar nuclear structure is seen near this axis in the opposite 

 half of the egg ; it is not, however, surrounded by pigment, but lies in 

 the yolk, from which it can be distinguished only with difficulty. Sub- 

 sequently both nuclei lie in the swollen end of the pigmented process, 

 and fuse into a single nucleus which now lies immediately surrounded 

 by a layer of finely granular protoplasm which is in turn enveloped in 

 the swollen end of the pigment process. This requires only about two 

 hours and a half from the time of fertilization. The interpretation 

 which Hertwig gives these observations is too evident to require their 

 formal statement. Never was more than one " pigment process " observed, 

 so that the penetration of only a single spermatozoon is probably normal. 

 The most important fact established by Hertwig, and one entirely 

 new for Batrachia, is the existence of an " egg nucleus " which ulti- 

 mately unites with the "sperm nucleus." Concerning the origin of 

 the former, Hertwig says, it is quite probable that so inconspicuous a 

 structure should have existed and been overlooked before the stage at 

 which he first saw it. From its minuteness it certainly cannot corre- 

 spond to the total mass of nuclear substance contained in the germina- 

 tive vesicle ; that, however, does not prevent its having descended 

 directly from such nuclear substance. The problem here is not, after all, 

 why so little nuclear substance is transferred to the female pronucleus 

 (Eikern), but what signification has the m?^/^?"nucleolar, as compared with 

 the immucleolar condition of the germinative vesicle'? 



