722 THE PHYSIOLOGY OF REPRODUCTION 



Among fish, pike and carp are usually said to attain to great ages 

 and even to live for centuries, but there are few accurate data. 



Among reptiles, crocodiles and tortoises are known to have long 

 lives, a tortoise from the Galapagos Islands being stated to have lived 

 for 175 years. 



The length of life in birds has been discussed by Gurney, 1 who 

 cites several examples of great longevity, but the more usual duration 

 of life is from fifteen to twenty years. Canaries are stated to have 

 attained to twenty years of age, a herring gull to forty-four, an 

 imperial eagle to fifty-six, a heron to sixty, an eagle owl to sixty- 

 eight, a raven to sixty-nine, a swan to seventy, and a goose to eighty. 

 Hobday 2 has recently described a pair of ring-doves which lived to 



FIG. 188. Land tortoise (Testudo maiiritanica), aged at least 



eighty-six, belonging to M. Elie Metchnikoff. 

 (From Metchnikoff's The Prolongation of Life, by permission of Mr W. Heinemann.) 



be twenty-one, and then did not die a natural death. Metchnikoff' 

 records a case of a parrot which lived for eighty-two years. 



Mammals on the average appear to have considerably shorter 

 lives than birds. According to Weismann, whales live for some 

 hundreds of years, but it is difficult to see how this can be more than 

 an assumption. There can be little doubt that the great age assigned 

 by some of the older writers to elephants is mythical, and probably 

 150 years is almost the maximum ever attained. Horses in rare 

 cases have reached forty years, cattle somewhat over thirty, and 

 sheep over twenty years. A dog is said to have lived for thirty-four 

 years, but twenty is usually regarded as a great age for this animal. 

 Cats have been known to live to be twenty-one and even twenty- 

 three, but no greater ages appear to have been recorded. The white 

 rat may live forty months, or even longer, but the average age 



1 Gurney, " On the Comparative Ages to which Birds Live," Ibi, vol. v., 1899. 



2 Hobday, " An Instance of Longevity in Bing-Doves," Vet. Jour., vol. Ixxvi., 

 1920. 



