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. TJie Nucleus in Fertilisation 



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 embryo, 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 

 Riickert, 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 

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



sea-urchin. [Boveri.] ..... ,- , , , 



, T^ f Di . ■ ■ f 1 . J distribution of paternal and ma- 



A. Dwarf Pluteus arising from an enucleated ^ 



egg-fragment of Spharechinus gramdaris, fertil- tcmal chromatin tO all the Cclls of 



ized with spermatozoon of Echinus microtiiber- fVip offsorino" we find the ohvsio- 

 culatus, and showing purely paternal characters. . ,1^ • rt-ri. 



B. Normal Pluteus of Echinus microtuberculatus. loglCal explanation ot the tact that 



