CHAPTEE VIII. 



HEKEDITY. 



§ 80. Already^ in the last two chapters, the law of heredi- 

 tary transmission has been tacitly assumed; as, indeed, it 

 unavoidably is in all such discussions. Understood in its 

 entirety, the law is that each plant or animal, if it repro- 

 duces, gives origin to others like itself: the likeness consist- 

 ing, not so much in the repetition of individual traits as in the 

 assumption of the same general structure. This truth has 

 been rendered so familiar by daily illustration as almost to 

 have lost its significance. That wheat produces wheat — that 

 existing oxen have descended from ancestral oxen — that every 

 unfolding organism eventually takes the form of the class, 

 order, genus, and species from which it sprang; is a fact 

 which, by force of repetition, has acquired in our minds 

 almost the aspect of a necessity. It is in this, however, 

 that Heredity is principally displayed : the manifestations of 

 it commonly referred to being quite subordinate. And, as 

 thus understood, Heredity is universal. The various instances 

 of heterogenesis lately contemplated seem, indeed, to be at 

 variance with this assertion. But they are not really so. 

 Though the recurrence of like forms is, in these instances, 

 not direct but cyclical, still, the like forms do recur; and, 

 when taken together, the group of forms produced during one 

 of the cycles is as much like the groups produced in pre- 

 ceding cycles, as the single individual arising by homo- 

 genesis is like ancestral individuals. 



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