178 THE president's address. 



that is to say in all those organisms that constitute what I hav& 

 termed the cellular grade. Sex-phenomena appear, on the other 

 hand, to be quite absent in the organisms of the bacterial grade. 

 Certain processes of rearrangement of the chromatin-substance 

 in some of the bacterial organisms have been dignified with 

 the name of sexual processes, but they are quite different from 

 the union of two gametes seen in true syngamy. 



Much has been written, and many . theories have been put 

 forward, to explain the origin and significance of sex. I will 

 only mention one view briefly, that which is put forward by 

 Doflein in his great work on the Protozoa, a theory founded on 

 those enunciated previously by Hertwig and Schaudinn. The- 

 gist of this theory is as follows. Living cells are regarded as 

 consisting of two groups of vitally-active substances, the one- 

 regulating motor, the other trophic functions. In cell-repro- 

 duction by fission these substances are never distributed with 

 mathematical equality amongst the descendants, hence continued 

 reproduction of this kind brings about accumulations of difierent 

 properties in certain individuals, with, as a consequence, im- 

 paired vital activity and reproductive power. Individuals are 

 produced, some of which are richer in stored-up nutriment 

 (female), others in motile substance (male). Since these two- 

 kinds of individuals contain aggregations of substances which 

 have intense mutual chemical reactions, they exert an attraction 

 one towards the other ; the two individuals tend to unite as 

 gametes, and by their union cell-equilibrium is restored and vital 

 powers renewed. 



Hence syngamy is regarded as a necessity for the life-cycle^ 

 due primarily to the imperfections of cell-division, and to the 

 consequent loss of equilibrium in the cell-constituents. On thi& 

 view, the general absence of sex-phenomena in the lowest grade^ 

 and its existence in the higher, is readily intelligible. In the 

 bacterial grade, the body, usually very minute, is of extremely 

 simple structure, sometimes scarcely more than a speck of 

 chromatin ; in such organisms, inequalities of division, if they 

 occur, can be adjusted easily by the rearrangements of the 

 chromatin-substance already mentioned. On the other hand, 

 with the evolution of the cellular grade, the body is difierentiated 

 into at least two parts, nucleus and cytoplasm, and becomes of 

 increasingly complex structure; consequently an exact quantita- 



