No. 3-] FACTORS IN THE EVOLUTION OF MAMMALIA. 38 1 



tainly inadmissible to speak of such transmission as inconceiv- 

 able or as involving the operation of unknown forces. 



It is extremely difficult to obtain any satisfactory evidence of 

 the transmission of acquired characters, and this for two reasons. 

 In the first place, it is generally well-nigh impossible to determine 

 in any given instance whether a character is acquired or congen- 

 ital (employing the latter term to designate characters due to 

 changes in the germ-plasm itself). As a rule, it is taken for 

 granted that those structural features with which an animal is 

 born or hatched are altogether congenital, but nothing can be 

 more improbable ; for we know that embryos are very sensitive 

 to changed conditions, and are easily modified, but to determine 

 what characters are due to changes in the ovum and what to 

 modifications in the embryo, is a difficult matter. For my own 

 part, I am not inclined to attach much importance to the sup- 

 posed cases of transmitted mutilations, as from an a priori stand- 

 point they are improbable, and more especially because the long- 

 continued mutilations practised by many savage races appear to 

 be without result in this respect. Nevertheless, such facts as 

 those stated by Eimer (No. 15, p. 191) and DeCandolle (No. 14, 

 p. 94), from their own knowledge, and the experiments of 

 Obersteiner upon guinea-pigs, are not to be dismissed with a 

 sneer. Arbuthnot Lane has come to the conclusion "that a 

 force which produces no obvious change in the skeleton of the 

 antecedents, but only a tendency to change, can, acting as a 

 developmental factor, cause the apparently spontaneous devel- 

 opment of that change in the offspring" (No. 29, p. 215). It is 

 also well worthy of inquiry how far the extraordinary skill and 

 deftness of Japanese and other Oriental workmen is due to the 

 fact that handicrafts have long been hereditary in the same 

 families. 



Dall's position is an eminently reasonable one : "The conten- 

 tion of Weismann, that 'not a single fact hitherto brought 

 forward can be accepted as proof of the transmission of 

 acquired characters, demands attention. This reminds one of 

 the familiar statement of twenty years ago, that the Darwinians 

 had not brought forward a single instance of the conversion of 

 one species into another species. If the Dynamic Evolutionist 

 brings forward an hypothesis which explains the facts of nature 

 without violence to sound reasoning, that hypothesis is entitled 



