SIZE AND THE ELEMENTS. 73 



SECTION XIV. 



RELATIONS BETWEEN THE SIZE OF ANIMALS AND THE 

 MEDIUMS IN WHICH THEY LIVE. 



It lias just been remarked, that animals of different 

 types, even when living together, are framed in structures 

 of different size. Yet, life is so closely combined with 

 the elements of nature, that each type shows decided re- 

 lations, within its own limits, to these elements, as far as 

 size is concerned. 1 The aquatic Mammalia, as a whole, 

 are larger than the terrestrial ones ; so are the aquatic 

 Birds and the aquatic Eeptiles. In families which are 

 essentially terrestrial, the species which take to the water 

 are generally larger than those which remain permanently 

 terrestrial, as, for instance, the Polar Bear, the Beaver, the 

 Coypu, and the Capybara. Among the different families 

 of aquatic Birds, those of their representatives which are 

 more terrestrial in their habits are generally smaller than 

 those which live more permanently in the water. The same 

 relation is observed in the different families of Insects 

 which number aquatic and terrestrial species. It is 

 further remarkable, that, among aquatic animals, the 

 fresh- water types are inferior in size to the marine ones ; 

 the marine Turtles are all larger than the largest inhabi- 

 tants of our rivers and ponds ; the more aquatic Trionyx 

 larger than the Emyds ; and, among these, the more aquatic 

 Chelydra larger than the true Emys, and these generally 

 larger than the more terrestrial Clemmys or the Cistudo. 



1 GEOFPROY ST. HILAIRE (IsiD.), etc., quoted above, p. 46; and BE- 



Recherches zoologiques et physiolo- FOLD (A. TON), Untersuchungen liber 



giques sur les variations de la taille die Vertheilung von Wasser, orgau- 



chez les Aniniaux et dans les races ischer Materie und anorganischen 



humaines; Paris, 1831, 4to. See also VerbindungenirnThierreiche,Zeitsch. 



my paper upon the Natural Relations f. wiss. Zool., 1857, vol. 8, p. 487. 

 between Animals and the Elements, 



