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THE AMERICAN NATURALIST [Vol. XLlX 



correspond in heredity with the coat colors of mammals. 



A third great feature of Mendel's discovery is that in 

 such alternative pairs of characters as tallness and 

 dwarfness one may be dominant and the other recessive, 

 following in successive generations the well-established 

 Mendelian law. 



It remains to be observed whether any of the propor- 

 tional characters of mammals follow this law. 



It remains to be observed, also, whether rectigrada- 

 tional characters like the "pli caballin" in the grinding 

 teeth of the horse exhibit in heredity the Mendelian laws 

 of dominance and recession. This could only be ascer- 

 tained among mammals by observations on hybrids in 

 such a family as the Bovidae, which are fertile inter se, 21 

 or on similar characters in the hybrids between wild 

 natural breeds. 



The discovery through experiment by zoologists and 

 botanists that many saltation characters, such as sports 

 and abnormalities, follow the Mendelian law of domi- 

 nance and recession has led to the entirely unwarrant- 

 able assumption that only characters which are discon- 

 tinuous, or of sudden origin, are sharply separable in 

 heredity. This we have seen to be not in accord with 

 the facts, for the principle of separability is quite as 

 sharply defined in certain characters which have evolved 

 sloivly and continuously as in those which have evolved 

 suddenly. 



The special significance of recent Mendelian discov- 



21 Bartlett, A. D., ' ' Wild Animals in Captivity. ' ' 8vo. Chapman and 

 Hall, Ld. London, 1899, p. 219. "The two species of camel (Camelus 

 dromedarius and C. bactrianus) u ill breed together; the llama (Auchenia 

 glama) will breed with the alpaca (A. pacos), and the offspring are fertile. 

 Several species of deer, when crossed, produce fertile hybrids: for instance, 

 the Barbary deer (Cervus barbarus) with the red deer (C. elaphus), the 

 Mexican (C. mexicanus) with the Virginian deer (C. virginianus) . Several 



among the carnivora are well authenticated The lion (Fclis leo) has bred 

 with the tiger (F. tigris), the leopard (F. leopardus) with the jaguar (F. 

 onca), the wild cat (F. catus) with the domestic cat (F. domestica)." 



"Wild Beasts in the 'Zoo.' " 8vo. Chapman and Hall, Ld. London, 

 1900, pp. 71-72. "Hybrid Bovine Animals. ... In the first place, the bull 



