Influence of Heights and Depths. 17 



higher quadrupeds ; and, last only, Man, — at the head of the 

 creation, in time as well as in eminence, by structure, intel- 

 ligence, and moral endowments. 



Besides the general adaptation of animals to the surround- 

 ing media, there is a more special adaptation, which seems not 

 less important, though it is perhaps less striking. Animals, 

 as well as plants, do not live equally at all depths of the 

 ocean, or at all heights above its surface. There must be a 

 deep influence upon the geographical distribution of animals 

 in a vertical direction derived from atmospheric pressure 

 above the surface of the waters, and from the pressure of the 

 water itself at greater and greater depths, — the level of the 

 ocean, or a small elevation above its surface, or a shallow 

 depth under its surface, being the field of the most extensive 

 and intensive development of animal life. And it is not a 

 little remarkable that in the same classes we should find 

 lower types at greater depths in the ocean, and also lower 

 types at greater heights above. We will quote a few 

 examples, to shew how much we may expect from investiga- 

 tions pursued in this direction, for at present we have but 

 little information which can aid us in ascertaining the rela- 

 tionship between atmospheric and hydrostatic pressure and 

 the energies of animal life. 



Among Poll/pi, the higher forms, such as Actimce, are more 

 abundant in shallow water than the lower coral-forming 

 types. Among Medusae, the young are either attached to 

 the bottom,, or grow from the depth, while the perfect free 

 forms of these animals come to the surface. Among Echi- 

 nodennSj the Crinoids are deep-water forms ; free star-fishes 

 and Echini^ and, above all Holothtirice, living nearer the sur- 

 face. Among MolluscOj the Acephala, which are lowest, have 

 their lower types, — the Brachiopods, entirely confined to deep 

 waters ; the Monomy avians appear next, and, above them, 

 the D imy avians ; among these lattery th-e highest family, 

 the Nayades, rises above the level of the ocean into the fresh 

 waters, and extends even to considerable heights above the 

 sea, in lakes and rivers. A number of examples of all classes 

 should be mentioned, to shew that this is the universal case ; 

 as, for instance, among Cvustacea the Macvura are, in general 



VOL. XLIX. NO. XCVII. — JULY 1850. B 



