TRANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS 71 



There are, indeed, many of these passive parts among auimaLs ; 

 I need only recall the coloration of animals, the whole set of skeletal 

 parts, so diversely formed, of the Arthropods, the legs, wings, antennae, 

 spines, hairs, claws, and so on, none of which can be changed by the 

 inherited results of exercise, because they are no longer capable of 

 modification by exercise ; they are ready before they are used ; they 

 come into use only after they have been hardened by exposure to the 

 air, and are no longer plastic ; they are at most capable of being used 

 up or mutilated. Finally, even so convinced an advocate of the 

 Lamarckian principle as Herbert Spencer has stated that among 

 plants the great majority of characters and distinctive features 

 cannot be explained by it, but only through the principle of selec- 

 tion ; all the diverse protective arrangements of individual parts, 

 like thorns, bristles, hairs, the felt-hairs of certain leaves, the 

 shells of nuts, the fat and oil in seeds, the varied arrangements for 

 the dispersal of seeds, and so on, all operate by their presence 

 alone, not through any real activity which causes them to vary, 

 and the results of which might be transmitted. An acacia covered 

 all over with thorns seldom requires to use its weapons even once, 

 and if a hungry ruminant does prick itself on the thorns it is 

 only a few of these which are thus ' exercised,' the rest remain 

 untouched. 



But since all these parts have originated notwithstanding tlieir 

 passivity, there must be a principle which evokes them in relation 

 to the necessities of the conditions of life, and this can only be 

 natural selection, that is, the self-regulation of variations in reference 

 to utility. And if there is this principle, we require no other to 

 explain what is already explained. 



I can quite well understand, however, that many naturalists, 

 and especially pala3ontologists, find it difficult to accept this con- 

 clusion. If we think only of those parts that actively function, and 

 thus change by reason of their function, being strengthened by use 

 and weakened and diminished in size by disuse, and if, further, we 

 follow these parts through the history of whole geological epochs, 

 we may certainly get the impression that the exercise of the parts 

 has directly caused their phyletic evolution. The direction prescribed 

 by utility in the course of the individual life and in the phylogeny 

 is the same, and the intra-selection, that is, the selection of tissues 

 within the individual animal, leads towards the same improvements 

 as the selection of 'persons/ Thus it appears as if the pliyletic 

 variations followed those of the individual life, while in reaHty 

 the reverse is true; the changes arising from variations in the 



