distance; and it is to insure this advantage, I believe, that giraffes have acquired their strongly marked spots, as zebras have acquired their distinctive stripes, and hyaenas their similarly banded or dappled coats.  One must always remember that disguise may be carried a trifle too far, and that recognisability in the parents often gives the young and giddy a point in their favour.  For example, it seems certain that the general grey-brown tint of European rabbits serves to render them indistinguishable in a field of bracken, stubble, or dry grass.  How hard it is, either for man or hawk, to pick out rabbits so long as they sit still, in an English meadow!  But as soon as they begin to run towards their burrows the white patch by their tails inevitably betrays them; and this betrayal seems at first sight like a failure of adaptation.  Certainly many a rabbit must be spotted and shot, or killed by birds of prey, solely on account of that tell-tale white patch as he makes for his shelter.  Nevertheless, when we come to look closer, we can see, as Mr. Wallace acutely suggests, that the tell-tale patch has its function also.  On the first alarm the parent rabbits take to their heels at once, and run at any untoward sight or sound toward the safety of the burrow.  The white patch and the hoisted tail act as a danger-signal to the little bunnies, and direct them which way to escape the threatened misfortune.  The young ones take the hint at once and follow their leader.  Thus what may be sometimes a disadvantage to the individual animal becomes in the long run of incalculable benefit to the entire community.

It is interesting to note, too, how much alike in build and gait are these three thoroughbred desert roamers, the giraffe, the ostrich, and the camel or dromedary.  In their long legs, their stalking march, their tall necks, and their ungainly appearance they all betoken their common adaptation to the needs and demands of a special environment.  Since food is scarce and shelter rare, they have to run about much over large spaces in search of a livelihood or to escape their enemies.  Then the burning nature of the sand as well as the need for speed compels them to have long legs which in turn necessitate equally long necks, if they are to reach the ground or the trees overhead for food and drink.  Their feet have to be soft and padded to enable them to run over the sand with ease; and hard horny patches must protect their knees and all other portions of the body liable to touch the sweltering surface when they lie down to rest themselves.  Finally, they can all endure thirst for long periods together; and the camel, the most inveterate desert-haunter of the trio, is even provided with a special stomach to take in water for several days at a stretch, besides having a peculiarly tough skin in which perspiration is reduced to a minimum.  He carries his own water-supply internally, and wastes as little of it by the way as possible.