I855-] MUTABILITY OF SPECIES. 409 



I forget whether I ever told you what the object of my 

 present work is, — it is to view all facts that I can master 

 (eheu, eheu, how ignorant I find I am) in Natural History 

 (as on geographical distribution, palaeontology, classification, 

 hybridism, domestic animals and plants, &c, &c, &c.) to see 

 how far they favour or are opposed to the notion that wild 

 species are mutable or immutable : I mean with my utmost 

 power to give all arguments and facts on both sides. I have 

 a member of people helping me in every way, and giving me 

 most valuable assistance ; but I often doubt whether the sub- 

 ject will not quite overpower me. 



So much for the quasi-business part of my letter. I am 

 very very sorry to hear so indifferent account of your health : 

 with your large family your life is very precious, and I am 

 sure with all your activity and goodness it ought to be a 

 happy one, or as happy as can reasonably be expected with 

 all the cares of futurity on one. 



One cannot expect the present to be like the old Crux- 

 major days at the foot of those noble willow stumps, the 

 memory of which I revere. I now find my little entomology 

 which I wholly owe to you, comes in very useful. I am very 

 glad to hear that you have given yourself a rest from Sun- 

 day duties. How much illness you have had in your life ! 

 Farewell my dear Fox. I assure you I thank you heartily for 

 your proffered assistance."] 



C. Darwin to W. D. Fox. 



Down, May 7th [1855]. 

 My dear Fox, — My correspondence has cost you a deal 

 of trouble, though this note will not. I found yours on my 

 return home on Saturday after a week's work in London. 

 Whilst there I saw Yarrell, who told me he had carefully ex- 

 amined all points in the Call Duck, and did not feel any 

 doubt about it being specifically identical, and that it had 

 crossed freely with common varieties in St. James's Park. I 

 should therefore be very glad for a seven-days' duckling and 

 19 



