INTERMEDIATES AND MUTATION THEORY 2G9 



proved to occur in families bred from the same female 

 without the occurrence of any intermediates, and the 

 fact that the two segregate cleanly is strong evidence in 

 favour of the Mendelian view." 



In the case of the theoretical origin of wahlbergi from 

 mima the change in pattern is a large one, and it may 

 well be asked what are the chances against the proba- 

 bility of the dominicanus-wahlbergi pattern arising sud- 

 denly, complete, in two cases, from the very different 

 echeria-mima pattern, and in such a way that at one 

 step the new pattern is the same in the two new butter- 

 flies and differs in the same way from the parent pattern ! 



Moreover, the possibility of the same large variation 

 suddenly occurring in these different butterflies is rendered 

 still more remote by the fact that while mima and wahlbergi 

 are forms of one species, echeria and dominicanus are 

 different species of one genus and by no means closely 

 related within that genus. The two examples given are 

 therefore not analogous. 



Again, in Bedrock, vol. ii. Professor Punnett discusses 

 the polymorphic forms of the mimetic oriental " swallow- 

 tail " butterfly Papilio polytes. He says : " Mr. J. C. F. 

 Fryer has recently succeeded in carrying out an elaborate 

 series of breeding experiments with this species and has 

 shown that any form of female can produce any other 

 form provided that she mates with an appropriate male, 

 while in certain cases all three forms may appear in the 

 same brood. Even in such a case all the three forms 

 are sharply cut and clear, there being a complete absence 

 of intermediates or transitional forms." 



Incidentally it may be remarked in passing that had 

 Mr. Fryer worked with the African Papilio dardanus 

 there would not have been a complete absence of tran- 

 sitional forms. 



At first sight the Mendelian argument seems to be that 

 absence of intermediates is proof of origin by mutation. 



