ON SPECIES, HYBRIDS, AND VARIETIES. 171 



kept till, by tradition, it was supposed to be 100 years old." Some of 

 the huge Indian Tortoises, which have been kept, from time to time, in 

 the Gardens of the Zoological Society, London, could not have been 

 less than 200 years old, and, probably, much more, since their growth is 

 slow, and their size, when first hatched from the egg, small ; yet, some 

 have weighed upwards of 400 pounds. The same observations apply to 

 Crocodiles and huge Snakes, as Boas and Pythons ; but no well-authen- 

 ticated data have been obtained, upon which to form an estimate of their 

 longevity. An instance is known in which the common Snake (Tropido- 

 notus natrix) was kept eleven years in captivity ; but of the cause of its 

 death no account has been received.* The Toad is a long-lived animal ; 

 an instance is on record, of one having been kept, in a sort of half-domestic 

 state, for thirty-six years, when an accident caused its death. 



With respect to fishes, whose growth is slow, and whose skeleton 

 never attains the consistency which it does even in reptiles, still less that 

 which characterizes the bones of birds and Mammalia, their existence 

 seems to be remarkably enduring. They inhabit a medium much less 

 liable to sudden alterations of temperature than is the atmosphere, and their 

 muscular powers are very great. The Pike has been known to live 267 

 years ; the Carp, 200 ; without ending, even then, their existence accord- 

 ing to the course of nature. It is probable that the oceanic fishes enjoy a 

 still longer date of life than the fresh-water species ; but no data exist 

 upon which to draw out even a limited scale. 



Confining our observations to the Mammalia, it may be observed, that it 

 is difficult to reduce general rules to anything like universal application. It 

 may be stated, however, that the most prolific are, ordinarily, the shortest 

 lived. The smaller Mammalia, the Rodentia in particular, are very fertile ; 

 and their existence, on the average, is of short duration. -j- The fertility 

 of the Rodentia, however, is not so much intended as a counterbalance 

 to the natural death of the species, as to compensate for their destruction 

 by extrinsic causes ; for, so great is their loss by the agency of their preda- 

 tory foes, that, unless the numbers destroyed were rapidly recruited, the 

 annihilation of species would be in danger ; and, with their annihilation, -a 

 deficiency in that supply of food which they furnish to the Carnivora sub- 

 sisting upon them. On the other hand, it is reasonable to suppose that the 

 larger Mammalia, and more especially those which produce only a single 

 offspring in the course of every two years, will enjoy an extended duration 

 of existence : to a certain extent, such is the case. The age of the Ele- 

 phant, Rhinoceros, and Hippopotamus, is said to extend through centuries. 

 The Horse, however, is old at thirty, and so is the Ox : the age of the 

 Sheep is about fifteen years ; but none of these larger Herbivora produce, 



* The skin of this Snake, prepared and mounted, is in the Mus. Zool. Soc. L. 

 t The age of the Rabbit is from five to seven years. 



