180 THE president's ADDRESS. 



into distinct races and strains, either under the influence of 

 environment or by innate variations (if indeed there be any 

 variations in these organisms not due to environmental influences). 

 Syngamy tends to reduce the individual differences to a common 

 level, by mixing together the characters of divergent strains. 

 If this notion be correct, it follows that there are no true species 

 amongst organisms of the bacterial grade, if it be true that 

 syngamy does not occur amongst them ; the so-called species of 

 Bacteria are to be regarded as mere strains, capable of modifica- 

 tion in any direction by environmental influences, and without 

 the relatively much greater stability of a true species. Researches 

 that are now being carried on at the Lister Institute and else- 

 where, will, it may be hoped, throw light on the question of 

 the mutability of bacterial " species." 



From these considerations it is, I think, evident that the 

 passage from the bacterial to the cellular grade was perhaps the 

 most important advance in the evolution of living beings. The 

 acquisition of the cellular type of structure was the starting- 

 point for the evolution, not only of the higher groups of the 

 Protista, such as the Protozoa and unicellular plants, but through 

 them of the whole visible every-day world of animals and plants, 

 in all of which the cell is the unit of structure, and which 

 consist primarily of aggregates of cells. Further, with the 

 cellular type of structure were initiated, in my opinion, two of 

 the most universal and characteristic peculiarities of living 

 beings, namely, the phenomena of sex and the tendency to se- 

 gregate into species. 



In the present state of our knowledge it is necessary to pro- 

 ceed with extreme caution in attempting to deal with a group 

 of organisms in which so much remains to be discovered as in 

 the case of the Protista. I venture to bring forward these views 

 with the object of stimulating discussion and criticism, and of 

 indicating lines of inquiry that may be fruitful, and I desire 

 to direct attention to a standpoint from which it may be 

 possible in the future to survey the Protista, and perhaps to 

 bring them under a comprehensive and natural scheme of 

 classification. 



Joura, Queketl Microscopical Club, Ser. 2, Vol. XL, No. 6S, April 1911. 



