No. 590] THE EVOLUTION OF THE CELL 107 



In Aggregata also Dobell and Jameson have shown that 

 the union of the pronuclei in fertilization brings together 

 two sets each of six chromosomes, and that these then fuse 

 with one another in pairs according to tj^pe, that is to 

 say a with a, b with b, c with c, and so on. Analogous 

 phenomena have been demonstrated also in the gregarine 

 Diplospora, We have here a difference in detail, as com- 

 pared with the Metazoa, in that the fusion takes place at 

 the fertilization and not as the first step in the maturation 

 of the germ-cells ; but in both cases alike the fusion of 

 chromatin- elements individually distinct and exhibiting 

 specific characteristics is to be regarded as the final con- 

 summation of the sexual act, though long deferred in the 

 Metazoan life-cycle. 



As Vejdovsky has pointed out, there can be no more 

 striking evidence of the specific individuality of the 

 chromosomes than their fusion or copulation in relation 

 to the sexual act. Is there any other constant element or 

 constituent of living organisms exhibiting to anything like 

 the same degree the essentially vital characteristics of in- 

 dividuality manifested in specific behavior? If there is, 

 it remains to be discovered. 



I come now to the question of the permanence and im- 

 mortality, in the biological sense of the word, of the 

 chromatinic particles, which may be summarily stated as 

 follows: the chromatinic particles are the only constit- 

 uents of the cell which maintain persistently and uninter- 

 ruptedly their existence throughout the whole life-cycle of 

 living organisms universally. 



I hope I shall not be misunderstood when I enunciate 

 this apparently sweeping and breathless generalization. 

 I am perfectly aware that in the life-cycle of any given 

 species of organism there may be many cell-constituents 

 besides the chromatin-particles that are propagated con- 

 tinuously through the whole life-cycle; but cell-elements 

 which appear as constant parts of the organization of the 

 cell throughout the life-cycle in one type of organism may 

 be wanting altogether in other types. With the exception 



