810 NATURAL SCIENCE [May 



successfully with that arising from the sister-cell endowed with a 

 larger portion of chromatin. By continual elimination of the 

 varieties which produce unequal halving, necessarily at a disadvan- 

 tage if a moiety of their members tend continually to disappear, 

 there will ber established a variety in which the halving is exact : 

 tlie character of this variety being such that all its members aid the 

 permanent multiplication of the species. If, again, the case is that 

 of a metazoon, there will be the same eventual result. An animal 

 or plant, in which the chromatin is unequally divided among the 

 cells, must have tissues of uncertain formation. Assume that an 

 organ has, by survival of the fittest, been adjusted in the proportions 

 and qualities of its parts to a given function. If tlie multiplying 

 protoplasts, instead of taking equal portions of chromatin, have some 

 of them smaller portions, the parts of the organ formed of these, 

 developing less rapidly and having inferior energies, will throw the 

 organ out of adjustment, and the individual will suffer in the 

 struggle for life. That is to say, irregular division of the chromatin 

 will introduce a deranging factor, and natural selection will weed 

 out individuals in which it occurs. Of course no interpretation 

 is thus yielded of the special process known as karyokinesis. Prob- 

 ably other modes of equal division might have arisen. Here the 

 argument implies merely that the tendency of evolution is to estab- 

 lish some mode. In verification of the view that equal division 

 arises from the cause named, it is pointed out to me that amitosis, 

 which is a negation of mitosis or karyokinesis, occurs in transitory 

 tissues or diseased tissues, or where degeneracy is going on. 



But how does all this consist with the conclusion that the 

 chromatin conveys hereditary traits — that it is the vehicle in which 

 the constitutional structure, primarily of the species, and secondarily 

 of recent ancestors and parents, is represented ? To this question 

 there seems to be no definite answer. We may say only that this 

 second function is not necessarily in conflict with the first. While 

 the unstable units of chromatin, ever undergoing changes, diffuse 

 energy around, they may also be units which, under the conditions 

 furnished by fertilization, gravitate towards the organization of the 

 species. Possibly it may be that the complex combination of pro- 

 teids, common to chromatin and cytoplasm, is that part in which tlie 

 constitutional characters inhere ; while the phosphorised component, 

 falling from its unstable union and decomposing, evolves the energy 

 which, ordinarily the cause of changes, now excites the more active 

 changes following fertilisation. This suggestion harmonises with the 

 fact that the fertilisinn; substance which in animals constitutes the 

 head of the spermatozoon, and in plants that of the spermatozoid or 

 antherozoid, is distinguished from the other agents concerned by 

 having tlie highest proportion of the phosphorised element ; and it 



