382 SCOTT. [Vol. V. 



to respect and consideration until some better one is proposed 

 or some vitiating error detected in it " (No. 12, p. 7). When we 

 remember that evolution is a slow process, it is hardly to be ex- 

 pected that dynamic influences should be immediately apparent, 

 though the experiments on Artemia and on feeding caterpillars 

 point to a different conclusion. The question must be decided, 

 if at all, by the inductive method, by determining how the ob- 

 served facts can best be interpreted. 



When we turn to the hypotheses which Weismann proposes 

 in place of what Dall calls the dynamic theory, we might natu- 

 rally require the same rigid demonstration which he demands of 

 his opponents, but of such demonstration we find little, but rather 

 ingenious speculation. Although he has abandoned the view- 

 that sexual reproduction is the only factor in inducing variability, 

 he still appears to maintain that it is by far the most important. 

 " I am still of the opinion that the origin of sexual reproduction 

 depends upon the advantage which it affords to the operation of 

 natural selection ; nay, I am completely convinced that only 

 through its introduction was the higher development of the or- 

 ganic world possible. ... Even if, however, from our present 

 knowledge it is probable that sexual reproduction is not the sole 

 radical cause of variability in the Metazoa, still no one will dis- 

 pute that it is a most effective means of heightening variations, 

 and of mingling them in favorable proportions. I believe thit 

 the important part which this method of reproduction has 

 played in calling out the existing processes of selection, is hardly 

 diminished, even if one grants that direct influences upon the 

 idioplasm call forth a portion of individual variability " (No. 60, 

 p. 323). Weismann still maintains that somatogenic characters, 

 the effects of use and disuse, and the like, cannot be transmitted, 

 and attempts "to elucidate the phenomena without the aid of 

 this principle." 



But as Lloyd Morgan has pointed out, " by sexual admixture 

 alone, there can be no increase or decrease, beyond the mean of 

 the two parental forms. If, then, the union of sperm and ovum 

 be the source of new or more favorable variations, other than or 

 stronger than those of either parent, this must be due to the 

 fact that the hereditary tendencies not merely commingle, but, 

 under favorable conditions, combine, in some way different 

 indeed from, but perhaps analogous to, that exemplified in chem- 



