MAMMALS 105 



Darwin's authority was the French translation of the 

 Quadruples de Paraguay by Azara (vol. ii. p. 313, 1801). 

 That author says that he had heard as a certain fact that at 

 Santa Fe de la Vera Cruz there was born a horse on which 

 there grew behind the ears two horns, like those of bulls, 

 which acquired a length of over 4 inches, and which were 

 straight and pointed. Another similar horse was brought 

 from Chili to the house of the Alcade of Buenos Ayres where 

 many saw it. "II etoit doux et cependant il s'animait 

 quelquefois, et il se presentait comme le taureau pour frapper 

 de ses cornes." Some one took the horse in order to breed 

 from it, but the results had not been ascertained. A note 

 of the translator states that Hazard, in his translation of the 

 TraiU des Haras by Hartmann, says that he had been told 

 that in Spain there are special races of horses which have 

 for the most part one or two protuberances on the parietal 

 bones (sic) where the horns of cattle grow. 



The above is all the evidence, and it is obvious that it is 

 not very satisfactory. There is no statement by an actual 

 observer; all the assertions are made on the strength of 

 verbal and vague reports by others. No description of such 

 horns on the skulls of horses has been given, so far as I have 

 been able to discover, by a competent observer. At the 

 same time it is worth noting that the horse mentioned by 

 Azara is stated to have presented his horns when irritated, 

 like a bull. Therefore, if such a horned horse really existed, 

 it is at least possible that the action of striking with the 

 forehead preceded the development of the horns, and actually 

 was the cause of the development in the individual. With- 

 out more precise and definite evidence, however, it would 

 scarcely be profitable to devote further consideration to the 

 matter. 



Passing next to the even-toed ungulates which do not 

 ruminate, we find numerous cases of sexual dimorphism in 



