DURATION OF YOUTH IN MAMMALS 45 



my clothes. When it was angry it stamped with its fore-paws on 

 the ground. It had quite an unusual degree of character and 

 intelligence, and a most restless curiosity. 



The Odd-toed Ungulates, the rhinoceros, the horse and the tapir, 

 have a period of youth the length of which is roughly in proportion 

 to the size of the animals, but which is relatively rather shorter 

 than that of the elephant and the hyrax. A young rhinoceros 

 grows very quickly at first and runs with its mother until it is nearly 

 full grown. The hmit of size varies a good deal in the different 

 species, and actual growth appears to go on for a great many years, 

 but so far as can be ascertained the animals are adult at seven or 

 eight years of age. Horses and asses have been much influenced 

 by domestication, and the period of youth has been made shorter in 

 some of the breeds. Horses, asses and zebras are certainly adult at 

 five years of age, and the average duration of the period of youth is 

 less, probably from three to four years. Tapirs mature very 

 quickly ; when they are born they are striped and blotched with 

 white, so that they are very unlike their parents (see Plate VI, 

 p. 94). In four to six months this youthful coloration disappears 

 and they resemble their parents in pattern. The duration of 

 their youth is said to be under a year, a very short time for animals 

 of their size, but certainly some individuals at least continue to grow 

 for much more than a year. The rhinoceros and the tapir are 

 rather unintelligent animals with low mental powers. The horse 

 has been so much modified by association with man and by 

 selection for special qualities which are useful or pleasant that 

 we are disposed to have a false idea of its mental powers. I 

 rate them low as compared with monkeys, carnivores or even 

 elephants. 



The Even-toed Ungulates have a still shorter duration of youth in 

 proportion to their size. Those that do not ruminate, the hippo- 

 potamus and the swine and peccaries, have often bred in captivity, 

 and we have therefore accurate information about them. The 

 hippopotamus is a very large animal, a good male reaching over 

 14 feet in length and weighing well over 4 tons. They are fuUy 

 adult in five or six years, although they may continue to increase 

 in bulk for some time after that. Swine of different kinds come to 

 maturity in from eighteen months to two years, although they also 

 may continue to increase in size for a longer period. The hippo- 

 potamus is certainly a stupid animal, and I do not believe in the 

 intelligence of pigs. The tricks of trained animals, such as the 



