REVERSION. 169 
modes of heredity have been defined by Darwin, 
and yet more systematically by Haeckel, as “laws of 
inheritance,” and corroborated by them by a profu- 
sion of examples. If heredity may be termed the 
conservative element in the life of species, we may also 
speak in particular of a conservative heredity, by 
which the old, long-established characteristics and pe- 
culiarities are transferred. The more stubbornly a 
character is transmitted, or, what amounts to the same, 
the greater the number of families, genera, and species; 
over which a character is extended,. the more ancient 
must it be considered, the earlier did it appear in the 
ancestral stock. In most cases, this conservative he- 
redity 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 con- 
servative heredity may likewise display itself inter- 
mittently, either when merely individual characters of 
the ancestors reappear after lying dormant for one, 
several, or many generations,—a phenomenon desig- 
nated 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 
suspended in the parents. But most frequent and 
striking is the atavism of domestic animals and culti- 
vated plants, a stubborn antagonist to breeders. Of no 
domestic animal is the aboriginal stock known with such 
approximate certainty as that of the pigeon. Now there 
