384 DARWINISM TO-DAY. 



denser water condition. * But what of the extra abdominal 

 segment, the longer telson projections and their increased 

 hairiness, all of which as shown by Schmankewitsch 8 (how- 

 ever mistakenly this investigator may have interpreted his 

 results as examples of actual species modification) and 

 Anikin 9 for Artemia salina and by the writer 10 for Artemia 

 franciscanns, are the ontogenetic differences that varying 

 density of salt water actually produces in individuals of a 

 single Artemia species. These differences, these variations, 

 are of the sort that I am calling non-significant, non-adapt- 

 ive, non-reasonable. They would not be prophesied ; they 

 seem to have no reasonable correlation with the causes 

 which produce them. But they are actually the results or 

 effects of determined proximate causes which are extrinsic 

 or environmental. If now the logical argument (based on 

 identity of adaptive modification in individuals and in spe- 

 cies) for the transmutation of ontogenetic changes into 

 phyletic changes has any validity, then these non-adaptive, 

 indifferent modifications may be transmuted as well as the 

 adaptive ones, and thus hosts of trivial, non-adaptive indif- 

 ferent species differences be explained on this Lamarcko- 

 Eimerian basis as well as the obviously adaptive modifica- 

 tions. But I am not insisting on this sort of argument too 

 strongly. It is exactly the sort of argument upon which the 

 theory of natural selection chiefly rests, and I have cer- 

 tainly tried to make evident in this book my belief in the 

 danger of the substitution of this sort of logical or meta- 

 physical basis of belief in a theory for a scientific basis of 

 observation and experiment. 



Finally, let us ask ourselves why we have adopted the 



common belief that our search for a cause of variability is a 



A suggestion search for some so far unknown, some quite 



causeTf vSrii 6 new f actor or f orce in biology ? May it not be 

 tion, that the factor is already familiar to us ; so 



familiar indeed perhaps that we are esteeming it too simple 



