1849.] VARIABILITY. 397 



father aver that a fever, or any serious accident, as a broken 

 limb, will cause in a man all the intestinal worms to be evacu- 

 ated. Might not this possibly have been the case with the 

 flukes in their early state ? 



I hope you were none the worse for Southampton ; * I wish 

 I had seen you looking rather fatter. I enjoyed my week 

 extremely, and it did me good. I missed you the last few 

 days, and we never managed to see much of each other ; but 

 there were so many people there, that I for one hardly saw 

 anything of any one. Once again I thank you very cordially 

 for your kind present, and the pleasure it has given me, and 

 believe me, Ever most truly yours, 



C. Darwin. 



P.S. — I have quite forgotten to say how greatly interested 

 I was with your discussion on the statistics of animals : when 

 will Natural History be so perfect that such points as you 

 discuss will be perfectly known about any one animal ? 



C. Darwin to J. D. Hooker. 



Malvern, June 13 [1S49]. 



... At last I am going to press with a small poor first- 

 fruit of my confounded Cirripedia, viz. the fossil pedunculate 

 cirripedia. You ask what effect studying species has had on 

 my variation theories ; I do not think much — I have felt 

 some difficulties more. On the other hand, I have been 

 struck (and probably unfairly from the class) with the varia- 

 bility of every part in some slight degree of every species. 

 When the same organ is rigorously compared in many indi- 

 viduals, I always find some slight variability, and conse- 

 quently that the diagnosis of species from minute differences 

 is always dangerous. I had thought the same parts of the 

 same species more resemble (than they do anyhow in Cirri- 

 pedia) objects cast in the same mould. Systematic work 



* The meeting of the British Association. 



