l] OF THE EQUIDAE 9 



explanation of the course which led to the extinction of the 

 American horses will be found in the fact that after coming 

 to the end of their evolutionary tether in the attainment of 

 speed the sole means by which they could escape from their 

 enemies they fell an easy prey to one or more of these 

 animals, who meanwhile had succeeded in improving their 

 methods of warfare in the struggle of life. 



But it is obvious that if the great carnivorae had exter- 

 minated the horses, and thereby brought about their own 

 destruction, they would certainly have eaten up the bisons 

 and tapirs before they themselves had perished of hunger, for it 

 cannot be supposed that these animals escaped because they 

 were fleeter of foot than the Equidae. 



It may well be that the destruction of these American 

 horses was due not to the continual ravages of mighty carni- 

 vores, but to the insidious inroads of far meaner foes, for we 

 must not forget that there are no feral horses in Paraguay, 

 because an Hippobosca or an Oestrus attacks the umbilical 

 region of young foals, and produces ulcers, which invariably 

 cause death unless human aid is interposed 1 . 



I do not for a moment suggest that the extinction of all 



1 Col. Hamilton Smith, "The Horse," Naturalist's Library, Vol. xn. p. 248, 

 Edinburgh, 1841. Though Azara does not mention this in his Spanish version 

 (from which the English trans, was made), yet (English trans., p. 66) speaking of 

 the wild cattle of Paraguay he says that "from August to January, which is the 

 calving time, the cows are driven in Paraguay twice a week to the rodeo, in 

 order to free them from a certain worm which infests them, more especially the 

 calves, at the umbilicus, and to such an extent that, without this assistance, they 

 would inevitably perish. The same malady occurs in Corrientes and the 

 Pueblos of the Missions : but in Monte Video and Buenos Ayres it is so little 

 known that it demands no particular attention ; nor are the herds during the 

 above-mentioned months collected so frequently as usual, for the pregnant cows 

 might be injured thereby, and many of the young calves would be lost." My 

 friend Prof. Graham Kerr writes as follows: "The fly appears to be the 

 ordinary blow-fly, which lays its eggs in the drying-up end of the severed 

 umbilical cord and on the blood round it. The larvae hatch out in a few hours 

 and cause ulceration and the death of the calf. Estancieros regularly round up 

 the cattle every few days, and dress the calves affected with medicated glycerine. 

 I have not personally seen the maggots on calves, but I have seen them on adult 

 cows." Darwin cites Azara for the statement about the horses, but he used 

 Azara's French edition, and probably Col. Smith did the same, as we shall see 

 later on. 



