308 THE THEORIES OF EVOLUTION 



fled without any accumulation of infinitesimal varia- 

 tions. 



The phenomenon of discontinuous variation had 

 been observed for many years; many instances of it 

 were cited and designated as "sports" or freaks." 

 Darwin mentions many cases of discontinuous varia- 

 tion : black-shouldered peacocks distinguished not only 

 by their colouration but by their size, strength and 

 fecundity; dachshunds; ancon sheep presenting the 

 same peculiarities as dachshunds; Meauchamp sheep; 

 hornless Paraguayan cattle, etc. 



Since Darwin's days, many other examples of dis- 

 continuous variation made constant by heredity have 

 been noted, both in the animal and the vegetable king- 

 dom : ]\ T iata cattle, known also as bulldog cattle or flat- 

 nosed cattle, characterised by foreshortened nasal and 

 superior maxillary bones, the nose and upper lip re- 

 ceding considerably; single-hoofed pigs; albino ax- 

 olotls. In the vegetable kingdom there are plants 

 with striped, variegated or double flowers, and other 

 characters which, having once appeared, become 

 through transmission the starting point of new varie- 

 ties (striped larkspur, cinquefoil clover, etc.). 

 Those varieties which originate accidentally are espe- 

 cially frequent in cultivated species, as artificial selec- 

 tion, operated by man, maintains the heredity of the 

 new character by preventing cross-breeding which 

 might obliterate it. 



