366 THE BIOLOGY OF THE SEASONS 



the length of their life's tether without any trace of either 

 senility or senescence. They pass their climacteric of 

 vigour, it may be ; they may be old in years, but certainly 

 not in structure ; they pass off the scene with a violent 

 shove victims to violent death. It is impossible to tell 

 whether the vital energies were or were not really impaired, 

 but we know that in many fishes and reptiles, for instance, 

 which have lived long, and have in the end died violently, 

 there is not in their organs or tissues the least hint of senile 

 involution or even of senescence. 



In a special category must be ranked the immortal 

 simple animals which never grow old, which disappear 

 directly into other individualities like themselves ; of which 

 enough has already been said. 



Let us now see if we can make further progress towards 

 clearness by proceeding on a quite different tack, by 

 considering the great variety there is in the duration of 

 life. This has often been made the subject of popular 

 remark and of quite fanciful popular estimate. Weis- 

 mann quotes from Jacob Grimm an old German saying : 

 " A wren lives three years, a dog three times as long as a 

 wren, a horse three times as long as a dog, and a man three 

 times as long as a horse that is, eighty-one years. A 

 donkey attains three times the age of a man, a wild goose 

 three times that of a donkey, a crow three times that of 

 a wild goose, a deer three times that of a crow, and an 

 oak three times the age of a deer." It need hardly be 

 said that most of these figures are quite fictitious, e.g. the 

 estimate of the deer's duration of life at six thousand, and 

 the oak's at twenty thousand. By counting the wood rings 

 in some of the great Californian trees an age of two thousand 

 years and more has been estimated, but some say that 

 more than one double ring of wood is sometimes formed in 

 one year. 



