56 GERMINAL SELECTION. 



less, for this process can be carried on to almost any 

 extent without the rest of the body necessarily becom- 

 ing involved in sympathetic alteration. Whole mem- 

 bers may become rudimentary, like the hind limbs 

 of the whale, or it may be only single toes or parts of 

 toes; the whole wing may degenerate in the females 

 of a butterfly species, or only a small circular group 

 of wing-scales, in the place of which a so-called "win- 

 dow" arises. A single vein of the wing also may de- 

 generate and disappear, or the process may affect only 

 a part of it, and this may happen in one sex only 

 of a species. In such cases the rest of the body may 

 remain absolutely unaltered ; only a stone is taken out 

 of the mosaic. 



The assumption, thus, appears to me irresistible, 

 that every such hereditary and likewise independent 

 and very slight change of the body rests on some 

 alteration of a single definite particle of the germinal 

 substance, and not as Spencer and his followers would 

 have it, on a change of all the units of the germ. If 

 the germinal substance consisted wholly of like units, 

 then in every change, were it only of a single char- 

 acter, each of these units would have to undergo ex- 

 actly the same modification. Now I do not see how 

 this is possible. 



But it may be that Spencer's assumption is the 

 simpler one? Quite the contrary, its simplicity is 

 merely apparent. Whilst my theory needs for each 

 modification only a modification of one constitutional 

 element of the germ, that is, of one particle of the 

 germinal substance, according to Spencer every par- 

 ticle of that substance must change, for they are all 

 supposed to be and to remain alike. But seeing that 

 all hereditary differences, be they of individuals, races, 



