84 THE DATA OF BIOLOGY. 



greater correspondence thus established, must, other things 

 equal, show itself both in greater complexity of life, and 

 greater length of life — a truth which will be duly realized on 

 remembering that enormous mortality which prevails among 

 lowly- organized creatures, and that gradual increase of 

 longevity and diminution of fertility which we meet with on 

 ascending to creatures of higher and higher development. 



It must, however, be remarked, that while length and com- 

 plexity of life are, to a great extent, associated — while a 

 more extended correspondence in the successive changes, 

 commonly implies increased correspondence in the simul- 

 taneous changes ; yet it is not uniformly so. Between the 

 two great divisions of life — animal and vegetal — this contrast 

 by no means holds. A tree may live a thousand years, 

 though the simultaneous changes going on in it answer only 

 to the few chemical affinities in the air and the earth, and 

 though its serial changes answer only to those of day and 

 night, of the weather and the seasons. A tortoise, which 

 exhibits in a given time nothing like the number of internal 

 actions adjusted to external ones, that are exhibited by a dog, 

 yet lives far longer. The tree by its massive trunk, and the 

 tortoise by its hard carapace, are saved the necessity of re- 

 sponding to those many surrounding mechanical actions which 

 organisms not thus protected must respond to or die ; or 

 rather — the tree and the tortoise display in their structures, 

 certain simple statical relations adapted to meet countless 

 dynamical relations external to them. But notwithstanding 

 the qualifications suggested by such cases, it needs but to 

 compare a microscopic fungus with an oak, an animalcule 

 with a shark, a mouse with a man, to recognize the fact that 

 this increasing correspondence of its changes with those of 

 the environment, which characterizes progressing life, ha- 

 bitually shows itself at the same time in continuity and in 

 complication. 



Even were not the connexion between length of life and 

 complexity of life thus conspicuous, it would still be true 



