262 EVOLUTION [CHAP. IV 



Letter 186 aboriginally gall-makers, and bear the same relation to them 

 which Apathus 1 probably does to Bombus ? With respect to 

 dimorphism, you may like to hear that Dr. Hooker tells me 

 that a dioecious parasitic plant allied to Rafflesia has its two 

 sexes parasitic on two distinct species of the same genus of 

 plants ; so look out for some such case in the two forms 

 of Cynips. I have posted to you copies of my papers on 

 dimorphism. Leersia 2 does behave in a state of nature in 

 the provoking manner described by me. With respect to 

 Wagner's curious discovery my opinion is worth nothing ; 

 no doubt it is a great anomaly, but it does not appear to me 

 nearly so incredible as to you. Remember how allied forms 

 in the Hydrozoa differ in their so-called alternate generations ; 

 I follow those naturalists who look at all such cases as forms 

 of gemmation ; and a multitude of organisms have this power 

 or traces of this power at all ages from the germ to maturity. 

 With respect to Agassiz's views, there were many, and there 

 are still not a few, who believe that the same species is created 

 on many spots. I wrote to Bates, and he will send you his 

 mimetic paper ; and I dare say others : he is a first-rate man. 

 Your case of the wingless insects near the Rocky 

 Mountains is extremely curious. I am sure I have heard 

 of some such case in the Old World : I think on the Caucasus. 

 Would not my argument about wingless insular insects 

 perhaps apply to truly Alpine insects ? for would it not be 

 destruction to them to be blown from their proper home? 

 I should like to'write on many points at greater length to you, 

 but I have no strength to spare. 



Letter 187 To A. R. Wallace. 



Down, Sept. 22nd [1865]. 



I am much obliged for your extract ; 3 I never heard of 

 such a case, though such a variation is perhaps the most 



1 Apathus (= Psithyrus) lives in the nests of Bombus. These insects 

 are said to be so like humble bees that "they were not distinguished 

 from them by the earlier entomologists : " Dr. Sharp in Cambridge Nat. 

 Hist. (Insects, Pt. II.), p. 59. 



2 Leersia oryzoides was for a long time thought to produce only 

 cleistogamic and therefore autogamous flowers. See Variation of 

 Animals and Plants, Ed. II., Vol. II., p. 69. 



3 Mr. Wallace had sent Darwin a note about a tufted cock-blackbird, 

 which transmitted the character to some of its offspring. 



