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 Ahicleus in Fertilization 



The foregoing argument receives an overwhelming reenforcement 

 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 offspring 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 embrvo, and 

 probably to all later-formed cells. 

 The latter conclusion, which long 

 remained a mere surmise, has been 

 rendered nearly a certainty by 

 the remarkable observations of 

 Ruckert, Zoja, and Hacker, de- 

 scribed in Chapters IV. and VI. 

 We must therefore accept the high 

 probability of the conclusion that 

 the specific character of the cell is 

 in the last analysis determined by 

 that of the nucleus, that is by the 

 chromatin, and that in the equal 

 distribution of paternal and ma- 

 egg-fragment of Sphcer echinus granular is, fertil- tcmal chromatin tO all the CClls of 

 ized with spermatozoon of Echinus microtuber- ^j^^ offsprinP" We find the physio- 

 culatus, ana showing purely paternal characters. . ,1 • r ■, r \ 



B. Normal Pluteus of Echinus microtuberculatus. loglCal explanation of the fact that 



Fig. 164. — Normal and dwarf larvae of the 

 sea-urchin. [BOVERI.] 



A. Dwarf Pluteus arising from an enucleated 



