198 GENETICS 



part of the digestive apparatus of many animals but 

 fraught so often with evil consequences to man; these 

 and scores of similar characters, which, taken together, 

 make man in the eyes of the comparative anatomist a 

 veritable old curiosity shop of ancestral relics, are the 

 last traces of characters which formerly had a sig- 

 nificance in some of man's forbears. Having lost their 

 usefulness, these structures still hang on to the ana- 

 tomical household as pensioners. They have not been 

 recalled from the past, but have always been with us, 

 although of diminishing importance. In no sense, 

 therefore, can they be called reversions. 



C. ACQUIRED CHARACTERS RESEMBLING ANCESTRAL ONES 



Sometimes the drunken descendant of a drunken 

 great-grandparent has acquired this characteristic 

 through his own initiative quite aside from any ances- 

 tral contribution to his germplasm. This is not rever- 

 sion, but reacquisition resembling the ancestral con- 

 dition. 



Again, tame animals that run wild acquire habits 

 resembling those of their wild ancestors, but this is 

 not necessarily reversion. It is the natural response 

 of feral animals to the conditions of wild life. 



D. CONVERGENT VARIATION 



The European hedgehog, Erinaceus, an insectivore, 

 the American porcupine, Erithizon, a rodent, and the 

 Australian spiny anteater, Echidna, a monotreme, are 

 all mammals which have developed in a similar manner 



