MAMMALS WITH CONTRASTED COLOURS 143 



Some Horses, as I said, show a light-coloured abdomen and 

 inner aspect of legs, but this is not common. Usually the lighter 

 colour is very partial, and nothing like what it is in the domestic 

 Ass, or the Black Buck. See Grevy's Zebra, fig. 52. 



Dr. Wallace, I think, is partly right and partly wrong, when he 

 says that the Rabbit has acquired the white colour on the under- 

 side of its tail by natural selection, so that it might use it as a 

 danger-signal. In my judgment it got the white colour by 

 inheritance from a remote ancestral unarmoured surface, the white 

 colour being a vestige of that ; while it may have acquired the 

 habit of turning up its tail, and showing the white banner, through 

 natural selection. We know, too, that other animals, under the 

 excitement of fear or anger, cock up their tail, so that it is no 

 wonder the Rabbit should do the same. The survival of those that 

 could perform this social function would follow as a consequence. 

 The Rabbit is a defenceless and timid animal. For its safety it has 

 to depend on its large ears, in addition to the faculty of running 

 into holes when its ears declare that possible enemies are about ; 

 and turning up its white surfaced tail, when running home in the 

 uncertain light of the dusk, may be a very useful way of showing its 

 associates which way the holes lie. 



This theory I am advocating will also explain why the front or 

 exterior aspects of all the legs of many animals are so often, 

 especially in Gazelles, differently coloured from the posterior or 

 inner aspects. Naturally the front and outer aspects of the limbs, 

 which received the brunt of the enemy's attacks, would have been 

 differently, armoured from the posterior and iniier aspects. This is 

 the state of things in certain Pangolins, for instance. Something 

 may perhaps also be due to the likelihood of there being only a 

 limited amount pf armour-material in the blood, and only those 

 parts which urgently needed protection could be supplied with it. 



