HYBRIDS BETWEEN THE HORSE AND ASS. 277 



smooth as glass, and can consequently take the brilliant polish 

 which is greatly esteemed by these beaux sadreurs. I need 

 hardly say that the leather which is thus employed, is worn 

 inside out It is both air and water tight The *' shell" is 

 connected to the skin so closely that the two form one piece ; 

 although their respective consistencies are different. If a 

 section be made through the hide, their line of union may be 

 readily seen In the ass, the *' shell" is not confined to the 

 skin that covers the pelvis ; but also extends over the ribs, 

 which are consequently not as sensitive to the effects of blows 

 as are those of the horse. I may point out that the tendency 

 which a horse has to turn his rump, as the least sensitive 

 part of his anatomy, towards falling rain, cold currents of 

 wind, etc., appears to be due to the feeling of protection to 

 that part, which the presence of the " shell '' on each side 

 gives him. 



Huxley remarks that asses form a distinct species from 

 horses ; because '' all asses have tufted tails and have callosi- 

 ties only on the inner side of the fore legs. If animals were 

 discovered having the general characters of the horse, but 

 sometimes with callosities only on the fore legs and more 

 or less tufted tails ; or animals having the general characters 

 of the ass, but with more or less bushy tails and sometimes 

 with callosities on both pairs of legs, besides being inter- 

 mediate in other respects, the two species would have to be 

 merged into one They could no longer be regarded as 

 morphologically distinct species, for they would not be dis- 

 tinctly definable one from the other/* When Huxley wrote 

 this, he was evidently unaware that the horse has not 

 invariably callosities on all four legs (p. 193). 



Hybrids between the Horse and Ass. — Neither the 

 mule (the produce of the jackass and mare), nor the hinny 

 or jennet (the cross between the horse and the she-ass), is 

 fertile, either among themselves, or with other members of 

 the horse family. Those animals which have been mistaken 

 by superficial observers as fertile mules, have been, I venture 



