Origin of Sexuality 265 



In such cases it seems that a definite chemical agent can 

 recoup the protoplasm, and through it the chromatin sub- 

 stance, in energy supply; that the chromatin or cognitic energy 

 therefore becomes "recharged in amount to a greater or less 

 degree, according to the nature of the nutritive material. The 

 phenomenon then is one, in which so much colloid substance 

 holds a definite supply of some highly complex and perfect 

 form of energy, as an intramolecular charge. This, in the 

 cases above cited, and in many beside if we judge from known 

 conditions of life, daily becomes so piled up in amount through 

 supply of normal food constituents that it gradually rearranges 

 and then drives asunder the inert but definitely linked mole- 

 cules of chromatin, and in turn reacts on the protoplasm so 

 as to rearrange and subdivide it into oppositely charged masses. 



With such Aaews on cell divisions before us we can now 

 compare sexual differentiation and sex-cells in ascending stages 

 of evolution. 



Sexuality in the Algce — Immediately above the Blue-green 

 Algae, and sho^\ang many affinities with them in the simpler 

 genera, are several large groups of green algae, that may be 

 classed into two main series, each showing lines of advancing 

 but diverging evolution. These can be distinguished as the 

 Conjugatae and the Zoogametse. The former includes the 

 desmids, the higher Conjugatse and the diatoms, in all of which 

 division, \^'ith or ^^^[thout subsequent separation of cells, is 

 the only or most frequent means of vegetative multiplication, 

 but in which, at very exact periods usually, the cell individuals 

 or chains of cells cease to be vegetative, and conjugate union 

 occurs between them. 



The latter includes the Protococcacese, Pleurococcaceae, 

 Tetrasporacese, Ulothricacese, Chaetophoraceje and other 

 groups (p. 308), in all of which division as well as other modes 

 of cell multiplication may occur, but in which at very exact 

 periods usually, and nearly always after formation of swarm- 

 spores or zoospores, the actively motile zoospores differentiate 

 in time as gamete cells and conjugate. 



Regarding these two groups, the tendency in recent years 

 has been to ignore the former and to emphasize the latter 



9* 



