IX THE HISTORY AND SCOPE OF ZOOLOGY 307 



its results the reformation and rehabilitation of Tele- 

 ology. According to that theory, every organ, every 

 part, colour, and peculiarity of an organism, must 

 either be of benefit to that organism itself, or have 

 been so to its ancestors : l no peculiarity of structure 

 or general conformation, no habit or instinct in any 

 organism, can be supposed to exist for the benefit or 

 amusement of another organism, not even for the 

 delectation of man himself. Necessarily, according to 

 the theory of natural selection, structures either are 

 present because they are selected as useful, or because 

 they are still inherited from ancestors to whom they 

 were useful, though no longer useful to the existing 

 representatives of those ancestors. 



The conception thus put forward entirely re- 

 founded Teleology. Structures previously inexplic- 

 able were explained as survivals from a past age, no 

 longer useful though once of value. Every variety of 

 form and colour was urgently and absolutely called 

 upon to produce its title to existence either as an 

 active useful agent or as a survival. Darwin himself 

 spent a large part of the later years of his life in thus 

 extending the new Teleology. A beginning only has 

 as yet been made in the new life of that branch of 

 zoological and botanical study. 



1 At the same time the fact that a useless variation of one part or 

 organ may be a necessary accompaniment of a useful variation of 

 another part or organ, was pointed out by Darwin, who applied the 

 terms " correlation of variation," and " correlation of growth " to this 

 phenomenon. The importance of the " solidarity " of the constituent 

 parts of the organism can scarcely be over-estimated : it was recognised 

 in other terms by Guvier and the earlier morphologists. 



