REVERSION. 169 



modes of heredity have been defined by Darwin, and 

 yet more systematically by Haeckel, as " laws of in- 

 heritance," and corroborated by them by a profusion 

 of examples. If heredity may be termed the conserva- 

 tive element in the life of species, we may also speak 

 in particular of a conservative heredity, by which the 

 old, long-established characteristics and peculiarities are 

 transferred. The more stubbornly a character is trans- 

 mitted, or, what amounts to the same, the greater the 

 number of famiHes, genera, and species, over which a 

 character is extended, the more ancient must it be con- 

 sidered, the earlier did it appear in the ancestral stock. 

 In most cases, this conservative heredity occurs in an 

 unbroken succession of generations, an observation on 

 which it is needless to enlarge, as it may be daily made by 

 every one. But conservative heredity may likewise dis- 

 play itself intermittently, either when merely individual 

 characters of the ancestors reappear after lying dormant 

 for one, several, or many generations, — a phenomenon 

 designated as Atavism, or reversion, — or when the species 

 is composed of a regular alternation of variously con- 

 stituted generations and individuals. This particular 

 sort of reversion is termed Alternate Generation, or 

 Heterogenesis. 



No one is surprised if children exhibit the bodily or 

 mental features of their grand-parents which were sus- 

 pended in the parents. But most frequent and striking 

 is the atavism of domestic animals and cultivated plants, 

 a stubborn antagonist to breeders. Of no domestic ani- 

 mal is the aboriginal stock known with such approximate 

 certainty as that of the pigeon. Now there are races 

 of pigeons purely bred for several centuries, and in 



