82 'DETERMINANTS' VERSUS 



somes are re-formed from exactly the same chromatin granules as 

 before. These phenomena of karyokinesis are well shown in 

 Fig. 74 of Weismann's " Evolution Theory," while the modification 

 of the process that occurs in fertilised eggs is equally well 

 shown in Fig. 75 of that work. 



If attention is concentrated upon this latter process it may be 

 easily understood that the fusion of the male nucleus with that of 

 the female nucleus should have given rise to the inference that 

 " these two nuclei convey respectively the paternal and maternal 

 traits which are mingled in the offspring. And when there came to 

 be discerned," as Herbert Spencer says,' " the karyokinesis by which 

 the chromatin is, during cell-fission, exactly halved between the 

 nuclei of the daughter-cells, the conclusion was drawn that the 

 chromatin is more especially the agent of inheritance." There is, 

 however, much cogency in what follows when he adds, "But 

 though, taken by themselves, the phenomena of fertilisation seem 

 to warrant this inference, the inference does not seem congruous 

 with the phenomena of ordinary cell-multiplication — phenomena 

 which have nothing to do with fertilisation and the transmission of 

 hereditary characters. No explanation is yielded by the fact that 

 ordinary cell-multiplication exhibits an elaborate process for exact 

 halving of the chromatin. Why should this substance be so care- 

 fully portioned out among the cells of tissues which are not even 

 remotely concerned with the propagation of the species ? If it be 

 said that the end achieved is the conveyance of paternal and 

 maternal qualities in equal degree to every tissue ; then the reply 

 is that they do not seem to be conveyed in equal degrees. In the 

 offspring there is not a uniform diffusion of the two sets of traits 

 throughout all parts, but an irregular mixture of traits of the one 

 with traits of the other." 



H. Spencer then proceeds to make a suggestion which is in 

 harmony with these facts, and well worthy of careful consideration. 

 He calls attention to the chemical composition of chromatin, and 

 its greater complexity compared with that of the general sub- 

 stance of the cell, seeing that analyses have shown it to contain 

 an organic acid (nucleic) rich in phosphorus, combined with an 

 albuminous substance : probably a combination of various proteids. 

 This nuclear substance, therefore, has a special instability and 

 tendency to undergo molecular change, such as nucleic acid has 



■ " Principles of Biology," 1898, Vol. I, p. 259. 



