86 l. VOLUTION [Chap. II 



Letter 43 on Aquilcgia : ' it has interested me much. It is exactly like 

 my barnacles ; but for my particular purpose, most unfortu- 

 nately, both Kolreuter and Gartner have worked chiefly on 

 A. vulgaris and canadensis and atro-purpurea, and these are 

 just the species that you seem not to have studied. N.B. 

 Why do you not let me buy the Indian Flora? You are 

 too magnificent. 



Now for a short ride on my chief (at present) hobby- 

 horse, viz. aberrant genera. What you say under your 

 remarks on Lepidodendron seems just the case that I want, 

 to give some sort of evidence of what we both believe in, viz. 

 how groups came to be anomalous or aberrant ; and I think 

 some sort of proof is required, for I do not believe very many 

 naturalists would at all admit our view. 



Thank you for the caution on large anomalous genera first 

 catching attention. I do not quite agree with your " grave 

 objection to the whole process," which is " that if you multiply 

 the anomalous species by ioo, and divide rhe normal by the 

 same, you will then reverse the names . . ." For, to take an 

 example, Ornithorhyncluts and EcJiidna would not be less 

 aberrant if each had a dozen (I do not say ioo, because we 

 have no such cases in the animal kingdom) species instead of 

 one. What would really make these two genera less anomalous 

 would be the creation of many genera and sub-families round 

 and radiating from them on all sides. Thus if Australia were 

 destroyed, Didelfhys in S. America would be wonderfully 

 anomalous (this is your case with Proteaceae), whereas now 

 there arc so many genera and little sub-families of Marsupiata 

 that the group cannot be called aberrant or anomalous. 

 Sagitta (and the earwig) is one of the most anomalous 

 animals in the world, and not a bit the less because there are 

 a dozen species. Now, my point (which, I think is a slightly 

 new point of view) is, if it is extinction which has made the 

 genus anomalous, as a general rule the same causes of extinc- 



1 This seems to refer to the discussion on the genus Aquilegia in Hooker 

 and Thomson's Flora Indica, 1855, Vol. I., Systematic Part, p. 44. The 

 authors' conclusion is that "all the European and many of the Siberian 

 forms generally recognised belong to one very variable species." With 

 regard to cirripedes, Mr. Darwin spoke of "certain just perceptible 

 differences which blend together and constitute varieties and not 

 species" (Life and Letters, I., p. 379). 



