DEGREE OF LIFE VARIES AS DEGREE OF CORRESPONDENCE. 103 



other things equal, show itself both in greater complexity of 

 life, and greater length of life: a truth which will be fully 

 perceived on remembering the enormous mortality which 

 prevails among lowly-organized creatures, and the gradual 

 increase of longevity and diminution of fertility which we 

 meet with on ascending to creatures of higher and higher 

 developments. 



It must be remarked, however, 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 

 responding 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 struc- 

 tures, certain simple statical relations adapted to meet 

 countless dynamical relations external to them. But not- 

 withstanding 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 progress- 

 ing life, habitually 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 

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