CIRRIPEDES. 



67 



writer was pleased to attribute the whole account to my fer- 

 tile imagination. The Cirripedes form a highly varying and 

 difficult group of species to class ; and my work was of con- 

 siderable use to me, when I had to discuss in the ' Origin of 

 Species ' the principles of a natural classification. Neverthe- 

 less, I doubt whether the work was worth the consumption of 

 so much time. 



From September 1854 I devoted my whole time to arrang- 

 ing my huge pile of notes, to observing, and to experiment- 

 ing in relation to the transmutation of species. During the 

 voyage of the Beagle I had been deeply impressed by discov- 

 ering in the Pampean formation great fossil animals covered 

 with armour like that on the existing armadillos ; secondly, 

 by the manner in which closely allied animals replace one 

 another in proceeding southwards over the Continent ; and 

 thirdly, by the South American character of most of the pro- 

 ductions of the Galapagos archipelago, and more especially 

 by the manner in which they differ slightly on each island of 

 the group ; none of the islands appearing to be very ancient 

 in a geological sense. 



It was evident that such facts as these, as well as many 

 others, could only be explained on the supposition that 

 species gradually become modified ; and the subject haunted 

 me. But it was equally evident that neither the action of the 

 surrounding conditions, nor the will of the organisms (espe- 

 cially in the case of plants) could account for the innumera- 

 ble cases in which organisms of every kind are beautifully 

 adapted to their habits of life for instance, a woodpecker or 

 a tree-frog to climb trees, or a seed for dispersal by hooks or 

 plumes. I had always been much struck by such adaptations, 

 and until these could be explained it seemed to me almost 

 useless to endeavour to prove by indirect evidence that 

 species have been modified. 



After my return to England it appeared to me that by 

 following the example of Lyell in Geology, and by collecting 

 all facts which bore in any way on the variation of animals 

 and plants under domestication and nature, some light might 



