2Z^ CLASSICS OF MODERN SCIENCE 



bird; — indeed, had the tuft appeared under domestication, it would 



have been called a monstrosity. 



ON THE DEGREE TO WHICH ORGANISATION TENDS TO ADVANCE 



Natural Selection acts exclusively by the preservation and accumu- 

 lation of variations, which are beneficial under the organic and in- 

 organic conditions to which each nature is exposed at all periods of 

 life. The ultimate result is that each creature tends to become more 

 and more improved in relation to its conditions. This improvement 

 inevitably leads to the gradual advancement of the organisation of 

 the greater number of living beings throughout the world. But 

 here we enter on a very intricate subject, for naturalists have not 

 defined to each other's satisfaction what is meant by an advance in 

 organisation. Amongst the vertebrata the degree of intellect and an 

 approach in structure to man clearly come into play. It might be 

 thought that the amount of change which the various parts and organs 

 pass through in their development from the embryo to maturity would 

 suffice as a standard of comparison ; but there are cases, as with 

 certain parasitic crustaceans, in which several parts of the structure 

 become less perfect, so that the mature animal cannot be called higher 

 than its larva. Von Bar's standard seems the most widely appli- 

 cable and the best, namely, the amount of differentiation of the parts 

 of the same organic being, in the adult state as I should be inclined 

 to add, and their specialisation for different functions ; or, as Milne 

 Edwards would express it, the completeness of the division of physio- 

 logical labour. But we shall see how obscure this subject is if we 

 look, for instance, to fishes, amongst which some naturalists rank those 

 as highest which, like the sharks, approach nearest to amphibians ; 

 whilst other naturalists rank the common bony or teleostean fishes as 

 the highest, inasmuch as they are most strictly fishlike, and differ 

 most from the other vertebrate classes. We see still more plainly the 

 obscurity of the subject by turning to plants, amongst which the 

 standard of intellect is of course quite excluded ; and here some 

 botanists rank those plants as highest which have every organ, as 

 sepals, petals, stamens, and pistils, fully developed in each flower; 

 whereas other botanists, probably with more truth, look at the plants 

 which have their several organs much modified and reduced in num- 

 ber as the highest. 



