270 STUDIES IN THE EVOLUTION OF ANIMALS 



where, still retain, and for which several other ruminants have 

 substituted tufts of long hair, or hair differently coloured from the 

 surrounding surface. Curiously enough, Grevy's Zebra has lost 

 the callosities from its legs entirely, without leaving any trace of 

 them, while the other Zebras and the Ass have them only on the 

 fore-legs, and the Horse has them on all four. So that the total 

 disappearance of callosities in many ruminants is no evidence 

 whatever that their ancestors never had them. I have not seen or 

 heard of any mention or trace of such a feature in Rhinoceroses, 

 Pigs, etc., to which the Horse is supposed to be closely allied. 



The ruminating apparatus of the Ox and its congeners may 

 appear a difficulty in the endeavour to approximate the two groups, 

 those of the Horse and of the ruminants ; but we know that there 

 is a section of Monkeys which have a stomach with several diver- 

 ticuli, and, curiously enough, this form of stomach seems to have 

 some relation to the absence of cheek-pouches, as if these acted 

 somewhat homologously with the crop of the bird and the rumen 

 of the ruminant. After all, these three features are diverticuli of 

 the digestive tube. 



We know that the Horse takes more time to masticate his food 

 than the Ox, and therefore does not require a ruminating organ. 

 It is not difficult to imagine that the ancestors of the Horse at one 

 time lived in a tract free from enemies, and therefore chewed their 

 food leisurely, and eventually got rid of the sacculated stomach, 

 if they previously had it ; or reversely, the ancestors of the Ox were 

 in tracts surrounded by enemies, and had to gobble their food and 

 depart as quickly as possible from the feeding-ground ; then those 

 who did not die of indigestion gradually got into the habit of 

 regurgitating their food and masticating it leisurely over again. 

 Of course all this was not done in a week. 



If one can imagine a Horse evolving out of a fish, there can 



