ATAVISM. 163 



retrograde modifications take place in consequence of 

 division of labour. 



Atavism, or reversion, must be regarded as a seventh 

 function of evolution, and, as sucb, plays no unimportant 

 part. In the evolution of almost every higher organism we 

 observe that the progressive completion of most organs is 

 accompanied by retrograde processes of evolution in single 

 parts. In the cell this retrograde metamorphosis usually 

 first occurs in consequence of the formation of fat-particles 

 in the protoplasm. The cell is destroyed by the fatty 

 degeneration of the protoplasm. During the course of 

 phylogenetic, as of ontogenetic evolution, whole organs may 

 thus retrograde by the dissolution of the cells which form 

 them. Thus, for example, during the evolution of the germ 

 of Man and of other Mammals, cartilages, muscles, etc., dis- 

 appear which were of great importance in our primitive 

 ancestors, the Fishes. This ontogenetic reversion reproduces, 

 owing to Heredity, a corresponding phylogenetic process. 

 The very interesting " rudimentary organs " are arrested — 

 bodily growths of this kind, traces of which still remain in 

 various stages of development (see p. 110). They are found 

 in nearly every higher many-celled organism attaining to 

 any considerable stage of evolution ; in this case the general 

 progress of the whole is scarcely ever conditional on the 

 equally progressive development of the cells ; on the con- 

 trary, certain cells perish during Ontogeny, while others 

 go on growing at their expense. This same phenomenon 

 is met with in human society. In this it is always the 

 case that many individuals perish without effecting any- 

 thing; while the majority constantly develop more or 

 less steadily. The comparison is perfectly apt. For the 



