352 



CELL-CHEMISTRY AND CELL-PHYSIOLOGY 



throughout the series of living forms, from the lowest to the highest, 

 that it must have a deep significance. And while we are not yet in 

 a position to grasp its full meaning, this contrast points unmistakably 

 to the conclusion that the most essential material handed on by the 

 mother-cell to its progeny is the chromatin, and that this substance 

 therefore has a special significance in inheritance. 



4. The Nucleus in Fertilization 



The foregoing argument receives an overwhelming reinforcement 

 from the facts of fertilization. Although the ovum supplies nearly 



all the cytoplasm for the embry- 

 onic body, and the spermatozoon 

 at most only a trace, the latter is 

 nevertheless as potent in its effect 

 on the off spring as the former. On 

 the other hand, the nuclei con- 

 tributed by the germ-cells, though 

 apparently different, become in 

 the end exactly equivalent in every 

 visible respect in structure, in 

 staining-reactions, and in the num- 

 ber and form of the chromosomes 

 to which each gives rise. But 

 furthermore the substance of the 

 two germ-nuclei is distributed with 

 absolute equality, certainly to the 

 first two cells of the embryo, and 

 / \/^^ \ probably to all later-formed cells. 



I V Jp^^l^ 1 1 The latter conclusion, which long 

 |j Jy* i^ |1 remained a mere surmise, has been 



I ^ wll rendered nearly a certainty by 



i J*% ^ e remar kable observations of 



IHr Riickert, Zoja, and Hacker, de- 



fell scribed in Chapters IV. and VI. 

 \ \ We must therefore accept the high 

 j'l probability of the conclusion that 

 the specific character of the cell is 

 If | in the last analysis determined by 

 M^ that of the nucleus, that is by the 

 Fig. 164. -Normal and dwarf larvae of the chromatin, and that in the equal 



sea-urchin. [BOVERI.] 



distribution of paternal and ma- 



A. Dwarf Pluteus arising from an enucleated 

 egg-fragment of Sphcerechinus granularis, fertil- 



ternal chromatin to all the cells of 



ized with spermatozoon of 'Echinus microtuber- the o ff sprmg we find the 

 ciilatus, and showing purely paternal characters. -11 rir-u 



B. Normal Pluteus of Echinus microtuberciilatus. logical explanation of the fact that 



