82 



EVOLUTION 



[CHAP. II 



Letter 40 Thank you for your abstract of your lecture at the Royal 

 Institution, which interested me much, and rather grieved 

 me, for I had hoped things had been in a slight degree 

 otherwise. 1 I heard some time ago that before long I might 

 congratulate you on becoming a married man. 2 From my 

 own experience of some fifteen years, I am very sure that 

 there is nothing in this wide world which more deserves con- 

 gratulation, and most sincerely and heartily do I congratulate 

 you, and wish you many years of as much happiness as 

 this world can afford. 



Letter 41 To J. D. Hooker. 



The following letter illustrates Darwin's work on aberrant genera. In 

 the Origin, Ed. I., p. 429, he wrote : " The more aberrant any form is, the 

 greater must be the number of connecting forms which, on my theory, 

 have been exterminated and utterly lost. And we have some evidence 

 of aberrant forms having suffered severely from extinction, for they are 

 generally represented by extremely few species ; and such species as do 

 occur are generally very distinct from each other, which again implies 

 extinction." 



Down, Nov. 1 5th [1855 ?]. 



In Schoenherr's Catalogue of Curculionidse, 3 the 6,717 

 species are on an average 10*17 to a genus. Waterhouse (who 

 knows the group well, and who has published on fewness 

 of species in aberrant genera) has given me a list of 62 

 aberrant genera, and these have on an average 7 '6 species; 

 and if one single genus be removed (and which I cannot yet 

 believe ought to be considered aberrant), then the 61 aberrant 



1 " On certain Zoological Arguments commonly adduced in favour of 

 the hypothesis of the Progressive Development of Animal Life," Dis- 

 course, Friday, April 20, 1855 : Proceedings R. I. (1855). Published also 

 in Huxley's Scientific Memoirs. The lecturer dwelt chiefly on the argu- 

 ment of Agassiz, which he summarises as follows : " Homocercal fishes 

 have in their embryonic state heterocercal tails ; therefore heterocercality 

 is, so far, a mark of an embryonic state as compared with homoce reality, 

 and the earlier heterocercal fish are embryonic as compared with the 

 later homocercal." He shows that facts do not support this view, and 

 concludes generally " that there is no real parallel between the successive 

 forms assumed in the development of the life of the individual at present 

 and those which have appeared at different epochs in the past." 



2 Mr. Huxley was married July 2ist, 1855. 



3 Genera et Species Curculionidum. (C. J. Schoenherr : Paris, 

 1833-38.) 



