282 Causes and Course of Organic Evolution 



multiplication, vegetative cells may directly become sex cells 

 by extrusion of certain chromatin constituents, and so of def- 

 inite amounts of some kind of energy. Such vegetative cells, 

 in becoming thus changed, may remain unaltered in size and 

 in general aspect, but undergo some fundamental change in 

 their store of chromatin and so of cognitic energy. These 

 are then termed isogametes. 



Such sexually different isogametes, when set free or brought 

 within measurable distance of each other, usually show power- 

 ful and exact attraction for each other and specially for the 

 chromatin substance, in a manner that can alone be explained 

 as due to their being charged by opposite or comj^lemental 

 amounts of energy that we would regard as cognitic. 



From such isogametes graded stages of evolving modifica- 

 tion can be traced in the size of each complemental sex cell, 

 till small forms are produced as sperm cells that consist almost 

 wholly of chromatin, and large forms are produced as eggs 

 that consist of a plasmatic and chromatin nucleus, also of 

 abundant protoplasm. These two are termed heterogametes. 

 Fusion of the relatively small chromatin sperm-mass with 

 the nucleus of the relatively large egg results in fertilization 

 and formation of a morphologically balanced individual, that 

 combines half of the characters of both parents. The extruded 

 material of each sex cell represents the remaining and super- 

 fluous half of the hereditary chromatin material. 



But till the Hsemoflagellata and the Infusoria are reached 

 there is no indication of cytological differentiation into sub- 

 stances, or separate chromatin and cell constituents, that 

 might in any sense be called somatoplasmic and germoplasmic 

 masses. In both of the above groups, however, there is strong 

 suggestion of a somatochromatin and a germochromatin 

 differentiation. Such is noteworthy from the standpoint of 

 heredity. 



The ])henomena of sexuality amongst the nucleate Algae 

 and the Protozoa, from their simplest beginnings, run closely 

 parallel, and suggest that the two groups of i)lants and animals 

 early diverged from a primitive and probably colorless holo- 



