ON SPECIES, HYBRIDS, AND VARIETIES. 175 



the Horse, the Ox, and the Camel, are examples ; and it is among 

 these animals of large size, ordinarily producing only one at a birth, 

 and, in a more advanced state of development than obtains among most 

 Mammalia, that the period of gestation is the longest. In the Elephant, 

 it endures for about twenty-three months ; in the Horse, upwards of 

 eleven months ; in the Tapir, between ten and eleven ; in the Drome- 

 dary, twelve ; in the Giraffe, upwards of fifteen months ; in the Cow, 

 nine ; in the females of the Red-deer, Fallow-deer, and Rein-deer, some- 

 what more than eight months. In the smaller ruminants, as the Sheep 

 and Goat, five months ; in the Sow, which produces a numerous litter, only 

 fourth months. In the Rodentia, which not only bring forth a numerous 

 progeny, but those, also, with the eyes closed, and in a very helpless con- 

 dition, or, in other words (though their development, after birth, is very 

 rapid), less matured, than are the young of the Horse, Ox, or Sheep, 

 the period of gestation is, comparatively, short ; in the Beaver (one of 

 the largest of the order), it endures for four months ; in the Rabbit and 

 Hare, from thirty to forty days ; in the Dormouse, thirty-one days ; in the 

 Guinea-pig, three weeks ; in the Squirrel and Rat, four weeks. Among 

 the larger Carnivora, the period of gestation is longer than among the 

 smaller species ; it endures for six months in the Bear ; 108 days in the 

 Lion ; seventy-nine days in the Puma ; nine weeks in the Arctic Fox ; 

 sixty-two or sixty-three days in the Dog ; fifty-five or fifty-six days in 

 the Cat ; in the Wolf, sixty- three days. The young of all the Carnivora 

 are born blind and helpless, and, like the young of the Rodentia, re- 

 quire a bed, or nest, for their reception ; their subsequent development 

 is slow ; and it is many months before they are able to rely upon their 

 independent exertions ; in the Dog, the eyelids begin to open about the 

 twelfth day ; and the permanent teeth are not fully acquired till after 

 the completion of a twelvemonth. Of all the Mammalia, the marsupials 

 have the shortest period of gestation, and produce their young in the 

 most rudimentary condition ; hence, the females, in most species, have 

 a fold of the skin of the abdomen, or a pouch, for the reception of 

 their young, and in which, attaching themselves to the teats, these semi- 

 foetal beings are fostered by her genial warmth, receive nutriment, and 

 grow ; nor, even when able to partake of other diet, in addition to the 

 mother's milk, do they, altogether, forsake this natural dormitory, but resort 

 to it, not only to obtain an occasional supply of milk, but, in times of 

 danger, as an asylum. The Kangaroo, the largest of marsupial ani- 

 mals, produces only a single offspring at a birth, after a period of gesta- 

 tion for thirty-nine days. The young, as observed by Professor Owen, 

 on the day of its birth, does not exceed one inch two lines from the nose 

 to the end of the tail ; its eyes are closed, and it resembles " an earth- 

 worm in the colour and semi-transparency of its integuments." At the 



