548 MAMMALS. 



according to Darwin, the rabbits introduced early in the 

 fifteenth century into Porto Santo, an island near Madeira, 

 are now represented by a dwarf race of about half the normal 

 size, and these are said to be incapable of breeding with the 

 ordinary forms. But the varieties with which we are familiar 

 in the breeds of tame rabbits, illustrate variation under 

 domestication and the efiScacy of artificial selection. 



External appearance. — The head bears long external ears 

 which are freely movable. The black patch at the tip of 

 the ears in the hare is either absent or very small in the 

 wild rabbit. This external ear is characteristic of most 

 Mammals, and seems to collect the sound like an ear- 

 trumpet. In the rabbit it is longitudinally folded, thin 

 and soft towards its tip, firm and cartilaginous at its base. 

 The large eyes have eyelids with few eyelashes, and a third 

 eyelid or nictitating membrane — a white fold of skin — lies 

 in the anterior corner. This third eyelid, the occurrence of 

 which we have already noticed in Reptiles and Birds, is pre- 

 sent in most Mammals, and is of use in cleaning the cornea. 

 It is absent in Cetaceans, where the front of the eye is bathed 

 by the water, and it is more or less rudimentary in man and 

 monkeys where the habitual winking of the upper eyelid makes 

 a nictitating membrane superfluous. The nostrils are, two 

 slits at the end of the snout, and are connected with the 

 mouth by a " hare-lip " cleft in the middle of the upper lip. 

 In front of the mouth are seen the chisel-edged incisors, a 

 pair on the mandibles, and two pairs on the premaxillse, — 

 the smaller pair lying behind the larger pair and concealed 

 by them. Through the toothless gap or diastema between the 

 front and back teeth, the hairy skin of the lips projects into 

 the mouth. On the sides of the snout, and about the eyes, 

 there are tactile hairs or vibrissse. 



The plump trunk is separated from the head by a short 

 neck. The tail is very short, but in the scampering wild 

 rabbit it is conspicuous as a white tuft, which some natu- 

 ralists interpret as a directive signal. Beneath the base of 

 the tail the food-canal ends, and beside the anus are the 

 openings of perineal glands, the secretion of which gives 

 the rabbit a characteristic odour. In front of the anus is 

 the urino-genital aperture, — in the male at the end of an 

 ensheathed penis, in the female a slit or vulva, with an 



