Origin of Sexuality 281 



in not a few cases been accurately observed. This, so far as 

 number of extruded and retained nuclei may form a criterion, 

 gives rise to seven degenerating and one persistent nucleus 

 in Paramoecium aurelia {82, 1: 390), to five degenerate and 

 one persistent in Dendrocometes, to three degenerate and one 

 persistent in female Vorticella, to seven degenerate and one 

 persistent in male VorticeUa, and to about seventy degenerate 

 and one persistent in Biirsaria sp. 



Reviewing the above, and related evidence that it would 

 be impossible to treat in detail here, it may be said for the 

 Protozoa, as for the main lines of Algae, that multiplication 

 may be effected by regular division, by budding, by rejuvenes- 

 cence, or by ency station with subsequent free cell formation. 

 In all of these cases the nucleo-nucleolar chromatin undergoes 

 division into definite chromosomes that are distributed to 

 each cell, and evidently bestow on it definite hereditary quali- 

 ties. 



Each division of a cell is apparently inaugurated by the 

 gradual accumulation of a store of bio-cognitic energy of like 

 sign or quality in the nuclear and nucleolar chromatin, up 

 to the stage when steady disruptive discharge occurs, and in 

 the process a redistribution of the plasmatic-chromatin mater- 

 ial occurs. So long as the environal conditions remain the 

 same, this process may be repeated up to a definite limit. 



Under normal conditions it has been shown for various 

 Infusoria and is probably true for many Protozoa, as it is for 

 most Algae, that after a limited number of divisions a senile 

 state is established, unless by change of en\dronal conditions 

 some new stimulus incites to continued division, or unless 

 sexual fusion of individuals, that had previously become sex- 

 ually differentiated, occurs. 



In the gradual evolution of sexuality moreover, this seems 

 always to be associated with chromatin formation, and is 

 absent or rudimentary in the simple bacteria and Blue-green 

 Algse, possibly also in the simi)lest animals. 



Subsequent to formation of chromatin material and result- 

 ing sex differentiation, and after a definite period of active 



