638 MAMMALIA. 



prolific, often breeding four to eight times in a year. It is 

 said to live, in normal conditions, seven or eight years. The 

 rabbit seems to have had its original home in the western 

 Mediterranean region, but it has spread widely throughout 

 Europe, and is now abundant in countries, such as Scotland 

 and Ireland, in which, a few generations ago, it was rare. 

 Introduced into Australia and New Zealand, it has multiplied 

 exceedingly, and has become a scourge. There are many 

 varieties of rabbit, some in isolated regions perhaps illustrat- 

 ing the effect of segregation in fostering divergent types. 

 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 efficacy 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 collects 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 eyes have 

 two eyelids with few eyelashes, and a third eyelid or nicti- 

 tating membrane — a white fold of skin — in the anterior upper 

 corner. This third eyelid, which also occurs in Reptiles 

 and Birds, is present 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 rudimentary 

 in man and monkeys, where its absence is compensated for 

 by the habitual winking of the upper eyelid. 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 pre- 

 maxillae — the smaller pair hidden behind the larger pair. 

 The first milk incisors above and below never cut the gum, 

 but are absorbed before birth ; the second milk incisors 

 above (there are none below) are functional, but are shed 

 about the third week of extra-uterine life ; the same is true 



