BY HEBEK A. LONGMAN. 27 



Other adaptive characters. Under the principle ot natural 

 selection, we may understand that it is an advantage for 

 certain skink and gecko lizards to be able to lose their 

 tails, but can we explain l)y the same process the power 

 of regenerating them ? It is difficult to diagnose the 

 actual origin of an organ, say, the limb of a vertebrate, 

 though once the limbs are there we can conceive a selective 

 process to modifications. We can comprehend that a 

 paddle has been independently evolved in turtles, penguins, 

 ichthyosaurs. seals and whales. Many naturalists assert 

 that minute variations, especially in their initial stages, 

 could not have a survival value. A jmrtial explanation 

 is Darwin's view of co-related variations. But actual facts 

 of variation greatly worried Darwin. As he quaintly 

 expressed himself when writing to Huxley : — "■ If. as I 

 think, external conditions produce little direct effect, what 

 the devil determines each particular variation \ " 



Writing of some cases of mimicry. R. H. Lock says, 

 ■ the brain reels before the task of picturing the gradual 

 building-up of such a resemblance by the successive 

 additions of small differences, each one useful to the poss- 

 essor of it."* 



We naturally look here to the Mutationists for informa- 

 tion and help. The principles associated by De Vries 

 with his well-known examples of mutation have recently 

 been subjected to much criticism. Several authorities 

 assert that the mutations noted of the Evening Primrose 

 {CEnothera lamarckiana) were in reality due to an ancestral 

 natural hybridism. The Onagracea? are evidently far more 

 susceptible to hybridising than most other orders. Prof. 

 E. C. Jeffrey, of Harvard University, even goes so far as 

 to say that the mutation theory "' may apparently be 

 now relegated to the limbo of discarded hypotheses. "f 

 But this is an unwarrantable dictum. Hybridism mav 

 be often associated with mutations, but it would be 

 exceedingly difficult to explain all mutations — especiallv, 

 as we shall see, those noted by palaeontologists — in this 

 way. There has been no mere repetition of '" repertoire 



*" \'ariati(>n, Heieclity and Evolution,'" ]>. .IT. 

 t" Science, " April 3rd, 1914. 



