I48 THE EVOLUTION OF LIVING BEINGS. 



some of the descendants of, the crossed invertebrates 

 — which descendants we then unite to the class of the 

 vertebrates — but be different in the segregates arisen 

 from them. 



So the different forms of extremities we meet with, in 

 different vertebrates, can be explained in a similar 

 way as the different forms and colors of flowers, viz by 

 segregation, and those existing now, are the rests of pro- 

 bably many others which have existed formerly, as 

 becomes evident upon comparison of the extremities 

 of the now existing reptils with those of former geo- 

 logical periods. 



The principle of selection holds good in as far as it 

 shows the result of the extermination by the struggle 

 for life; it shows us which forms could resist this, but 

 it is no principle which explains the origin of certain 

 types ; selection also spells extermination, the types 

 last to be exterminated, obtaining the epitheton ornans : 

 selected types. 



Consequently, we have to drop the idea of homology 

 in the sense of parts, occupying corresponding posi- 

 tions in the ancestral groundplan, but may continue 

 to use it, for convenience sake, cum grano salts, as in- 

 indicating corresponding positions in the general 

 groundplan, if we only keep in mind that such map- 

 ping out hasno other significance than as a pons asinorum 

 for our memory and never allows us, with certainty, to 

 distinguish between analogous and homologous parts 

 or between these and new formations, as is shown by the 

 example of the corollae, mentioned at the beginning of 

 this chapter. 



