218 



THE EVOLUTION THEORY 



not numerous other points in the animal also be hereditarily de- 

 terminable ? With such complexity of the invisible structure it would 

 not greatly surprise us if* we should find amphimixis occurring in all 

 unicellular organisms, and in many of them at a high level of elabora- 

 tion. These apparently lowly and simple organisms are obviously very 

 far from being the lowliest and simplest, as we shall discover later 

 in a different connexion. But that amphimixis is found as a periodi- 

 cally recurring process even among these, must depend upon the 

 fact that here too the preservation of the best-adapted structure, as 

 well as adaptability to new conditions, requires that the best variants 

 of many different parts of the cell should be brought together, and 

 since the hereditary substance lies in the ids of the luicleus, the union 



B 





FiG. 123. Conjugation of Coccicliimi j^roprium, a cellular parasite of the 

 newt {Triton), after Siedlecki. A, a microgamete {Ml) in the act of penetrat- 

 ing the shell of a macrogamete (Ma) through the micropyle. B, the male and 

 the female nuclear constituents are uniting <j c7ir and 9cJirj. 



of the ids of two unicellulars will make harmonious and many-side«l 

 adaptation materially easier. It will thus give an advantage in the 

 struggle for existence, and we may therefore expect to find that the 

 nuclear substance in all unicellular organism is made up of ids. 



The observations hitherto made do not, however, appear to bear 

 this out. for in the lower Flao-ellata and Alo-?e the nuclear sub- 

 stance does indeed consist of chromatin, but — as far as it can be made 

 out — of a compact unarranged mass of it. But even though deeper 

 investigations should succeed in demonstrating chromosomes in many 

 of these, the nucleus mitbt have arisen at some time, and we must 

 assume that it did so through a more intimate union of previously 

 loose aggregates of determinants, which were gradual^ arranged 

 and l)Ound together by the combining forces (affinities) we liave 



