56 EVOLUTION OF TO-DAY. 



had in his mind certain types in accordance with 

 which he created species. All animals and plants 

 created must be moulded according to one of the 

 types, although great variation could take place 

 within the type, and never exceeding its limits. 

 The type was, therefore, a purely ideal form exist- 

 ing only in the mind of the Creator. Of these types 

 Cuvier recognized four. But besides the great types, 

 it is necessary, in order to make the theory com- 

 plete, to assume that each class of animals was 

 made according to a sub-type, each order according 

 to a sub-sub type, and so on for families and genera. 

 Individuals could vary within the type of the species, 

 species within the type of the genus, genera within 

 the type of the family. The whole animal and vege- 

 table kingdoms are thus moulded in accordance 

 with many types and sub-types, each of which must 

 have existed in the mind of the Creator when he 

 created species. 



Modern scientists are, however, not satisfied with 

 this explanation, for reasons which will presently 

 appear, and have offered evolution as the explana- 

 tion sought. This theory claims that the likenesses 

 between animals are due to descent from common 

 ancestors ; that the well-known principle of heredity, 

 in accordance with which the child is like the parent, 

 is a sufficient explanation of classification and 

 homology. The classification of organisms is thus 

 simply arranging them according to their genetic 

 relationship : those animals showing the greatest 

 likeness having the most recent common ancestor ; 

 those more unlike being more distantly related ; 



