EFFECTS OF AMPFilMIXIS OX ONTOGKNY 273 



This is quite sufficient to deceive the birds which pursue the 

 butterfly, and a more accurate copy of the markings on a leaf 

 would not increase the deception ; for it only needs to be effec- 

 tive at a certain distance, and therefore has not increased in per- 

 fection, but has reached its limit at this stage. A precisely 

 similar occurrence must take place as regards the modification 

 of the ids of the germ-plasm if a new adaptation of the species is 

 concerned. In such a case, again, only a relative and not an 

 absolute perfection will be attained. The majority, but not all^ 

 of the ids may become modified by selection, while a minority 

 must accompany these through long periods and generations in 

 an unmodified or slightly modified condition. 



I have had to make this digression on the transformation of 

 species in its relation to the germ-plasm, in order that my ex- 

 planation of ' tJie 07itoge7ietic shifting of the hereditary resultant '' 

 may be comprehensible. It follows from the process of the 

 gradual transformation of the ids of germ-plasm and the trans- 

 ference of unmodified ids from one cell-generation to another, 

 that the ger77i-plasjn of every species must consist of a cojn- 

 binatioji of ids of a soinewhat different nature. For although 

 specific characters must have appeared simultaneously, and 

 many others must have arisen successively, in the course of 

 many generations, all the characters of the species will not be 

 represented by determinants in the same number of ids. The 

 oldest character, in fact, will be contained in almost all the 

 ids ; those which are somewhat younger, in a considerable 

 majority ; and still younger ones, perhaps also in a slight ma- 

 jority ; while those which have only just begun to be of use 

 to the species will only be present in a minority of the ids of 

 each individual. 



This circumstance is evidentlv connected with the degree of 

 variability of characters, which may, in fact, be a very different 

 one as regards the different characters of a species. Characters 

 on which selection is only beginning to act, can only be 

 represented by a majority of ids in a minority of individuals, 

 and the less variable characters are those which have been 

 selected for a greater number of generations, and are there- 

 fore present in a large number of ids of numerous individuals ; 

 and again, those characters which have long become definitely 

 fixed in all or almost all the individuals of a species, must be 



