, SUDDEN VARIATION 71 



makes a great difference). But when we speak of 

 &quot; correlative &quot; changes occurring suddenly in the 

 different parts of the eye, we use the word in an 

 entirely new sense : this time there is a whole set 

 of changes not only simultaneous, not only bound 

 together by community of origin, but so coordinated 

 that the organ keeps on performing the same simple 

 function, and even performs it better. That a change 

 in the germ, which influences the formation of the 

 retina, may affect at the same time also the formation 

 of the cornea, the iris, the lens, the visual centres, etc., 

 I admit, if necessary, although they are formations that 

 differ much more from one another in their original 

 nature than do probably hair and teeth. But that all 

 these simultaneous changes should occur in such a way 

 as to improve or even merely maintain vision, this is 

 what, in the hypothesis of sudden variation, I cannot 

 admit, unless a mysterious principle is to come in, 

 whose duty it is to watch over the interest of the 

 function. But this would be to give up the idea of 

 &quot; accidental &quot; variation. In reality, these two senses of 

 the word &quot; correlation &quot; are often interchanged in the 

 mind of the biologist, just like the two senses of the 

 word &quot;adaptation.&quot; And the confusion is almost 

 legitimate in botany, that science in which the theory 

 of the formation of species by sudden variation rests 

 on the firmest experimental basis. In vegetables, 

 function is far less narrowly bound to form than 

 in animals. Even profound morphological differences, 

 such as a change in the form of leaves, have no appreci 

 able influence on the exercise of function, and so do not 

 require a whole system of complementary changes for 

 the plant to remain fit to survive. But it is not so in 

 the animal, especially in the case of an organ like the eye, 



