272 THE GERM-PLASM 



acters — consists of a niunber of ideiitical ids, cannot be a strictly 

 correct one : the germ-piasfn tnust, on the contrary, contain a 

 majority of completely tnodified ids provided with new deter- 

 minants of the species, and of a jni?writy of ids of the ancestral 

 species which are only slightly or 7tot at all modified. The 

 number of the latter will diminish in the course of time in 

 consequence of selection of the individuals, and the new specific 

 characters will gradually lose their original variability. Owing 

 to natural selection, the germ-plasm will gradually be relieved of 

 those of its ids which have become only slightly or not at all 

 modified in the new direction, for those individuals in which it 

 still contains a large number of unmodified ids are as well 

 adapted as the others for the conditions of existence. As these 

 individuals are gradually eliminated in the struggle for existence, 

 the number of unmodified ids in the subsequent generations 

 must gradually become reduced; 2LX\d. this process of selectioji in 

 the germ-plasm will only reach a limit when the number of 

 unmodified or iiicompietely 7nodificd ids has become so small that 

 their influence on the development of the essential characters of 

 the species is inappreciable. 



This process of transformation of the ids of the germ-plasm 

 will, however, reach a limit, as do all processes of selection, w^hen 

 its continuance is no longer of any advantage. All adaptations 

 in an animal remain stationary and are not further perfected, 

 directly further improvement becomes useless ; and in the 

 same way the process of modification and elimination of the 

 ids, which forms the basis of other adaptations, will cease as soon 

 as the completely modified ids are present in such a majority 

 that the others can only exert an inappreciable influence on the 

 nature of the offspring. The useful and adaptable characters 

 will always undergo complete development in the normal process 

 of reproduction, — that is to say, in the intermingling of 

 individuals of the species, — even though some unmodified ids 

 may be present in the germ-plasm. Let us take as an example 

 the well-known case of the butterfly Kallima parallecta, which 

 resembles a leaf. The resemblance is very marked, although 

 not a complete one. The form of a leaf, with its midrib 

 and veins, — some regions appearing more or less faded, and 

 some dry or wet, and even of the appearance of a dewdrop, — is 

 indicated on the folded wings, but only certain of the secondary 

 veins on the right and left of the jniddle line are represented. 



