698 MAMMALIA. 
lemmings and marmots, also belong. Like the hare (Lepus 
timidus) and other species of the same genus, and like the 
Picas or tailless hares (Zagomys), the rabbit has two pairs of 
incisors in the upper jaw, while other Rodents have a single 
pair. Therefore the genera Lepus and Lagumys are some- 
times ranked as Duplicidentata, in contrast to all other 
Rodents (Simplicidentata). 
With the rabbit’s mode of life all are familiar. It is herb- 
ivorous, and often leaves softer food for the succulent bark 
of young trees; it is gregarious and a burrower; it is very 
prolific, frequently breeding four 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 regions, such as the High- 
lands of Scotland, 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 
