78 the president's address. 



before we can hope to reach even an approximate solution of the 

 problem. 



Some light may perhaps be thrown on the subject by ex- 

 periments such as those of Leduc and others upon artificial 

 osmotic growths. Leduc, in particular, has succeeded in pro- 

 ducing very interesting growth-forms by the osmotic action of 

 various chemical reagents in solution. Some of these forms bear 

 an extraordinary resemblance to the forms of living organisms. 

 I do not, of course, attribute much importance to the particular 

 forms produced in this manner as explaining the particular 

 forms of any living organisms. What they demonstrate is that 

 purely chemical and physical causes may give rise to more or less 

 definite and at the same time non -crystalline forms in colloidal 

 media, and though none of the forms as yet produced come 

 anywhere near our sponge-spicules in symmetry or sharpness of 

 definition, they certainly seem to indicate a hopeful line of 

 inquiry. The particular form produced depends upon the nature 

 of the reagents employed and upon the conditions under which 

 the experiment is carried out. If these always remain constant 

 we may assume that the osmotic growth will always have the same 

 form, but probably with the means at our disposal it would be 

 impossible to produce exactly the same result twice over. The 

 remarkable thing about the sponge microscleres is that within 

 the limits of the same species the same results very often are 

 exactly reproduced, or at any rate so exactly that we are unable 

 to distinguish between them. I suggest that these results are 

 produced by chemical and physical causes, involved in and 

 controlled by the hereditary constitution of the mother-cell, 

 and that any modification of this hereditary constitution must 

 give rise to a corresponding modification in the results. Further 

 than this I fear we cannot at present venture. 



It has frequently been objected to the theory of natural 

 selection that, however much useful characters may be en- 

 couraged and fostered in the struggle for existence, it cannot 

 account for the first appearance of such characters. This appears 

 to me to be a very fair criticism. It seems to me, also, very 

 misleading to speak of the origin of species by natural selection, 

 for specific characters throughout the animal and vegetable 

 kingdom are, I believe, generally non-adaptive, and therefore 

 cannot be directly due to natural selection. This is certainly the 



