AN ESS A V ON LONGEVITY. 17 



ever since. Others of equally vast age have been 

 observed in the waters of tropical America.' ^ If we 

 regard the whole product of the fertilized germ 

 as an individual, then we must conclude that these 

 corals have a longevity of more than 3000 years, 

 though we well know that countless generations 

 of asexually-produced polyps have succeeded one 

 another in these great coral masses. Without further 

 discussing the question here, we may adopt Mr. 

 Spencer's view, that there is no possible definition of 

 individual which is absolutely unobjectionable. ' In- 

 dividualities merge and are distributed, in such cases 

 as fusion and fission, which renders the estimation of 

 their longevity a matter of great indefiniteness, and 

 we shkll find it most agreeable to all the facts in 

 issue, to consider as individuals all those wholly or 

 partially independent organized masses which arise 

 by multicentral and multiaxial development that is 

 either continuous or discontinuous.' ^ 



The period of life which we must compare in dif- 

 ferent species is then that presented by individuals 

 as above defined. We have not to consider the life 

 of attached gemmae, nor of unlaid ova. Such life is 

 not the life of distinct individuals. Thus then, for our 

 purpose, all parts of a tree, as long as they remain 

 attached to the original axis, are but one individual. 

 But we have to consider and compare the duration 



' Leo Grindon : ' Life,' &c. p. 99. 



' ' Principles of Biology :' Spencer, vol. i. p. 207. 



c 



