156 



THE ORIGIN AND EVOLUTION OF LIFE 



parts, according to two laws: first, that each individual part 

 has its own mechanical evolution, and, second, that the same 

 mechanical problem is generally solved on the same principle. 



This, we observe, is invariably 

 the ideal principle, for, unlike 

 man, nature wastes little time 

 on inferior inventions but imme- 

 diately proceeds to superior in- 

 ventions. 



The three mechanical prob- 

 lems of existence in the water 

 habitat are: First, overcoming 

 the buoyancy of water either by 

 weighting down and increasing 

 the gravity of the body or by 

 the development of special grav- 

 itating organs, which enable 

 animals to rise and descend in 

 this medium; second, the me- 

 chanical problem of overcom- 

 ing the resistance of water in 

 rapid motion, which is accom- 

 plished by means of warped sur- 

 faces and well-designed entrant 

 and re-entrant angles of the 

 body similar to the ''stream- 

 lines" of the fastest modern 

 yachts; third, the problem of 

 propulsion of the body, which is 

 accomplished, first, by sinuous motion of the entire body, ter- 

 minating in powerful propulsion by the tail fin; secondly, by 

 supplementary action of the four lateral fins; third, by the 



HABITAT ADAPTATIONS OF THE VER- 

 TEBRATES TO THE CHANGES OF 

 ENVIRONMENT 



AERIAL 



(flying, volant types) 



AERO-ARBOREAL 



^PARACHUTE, VOLPLANING TYPEs) 



ARBOREAL 



^CLIMBING, LEAPING, AND BRACHIATING TYPEs) 



ARBOREO-TERRESTRIAL 



(walking and CLIMBING, SCANSORIAL TYPEsJ 



TERRESTRIAL 



(ambulatory, slow: cursoria 

 saltatory, leaping ; ghavipoht 

 cumbrous) 



TERRESTRIO-FOSSOHIAL 



(walking AND BURROWING TYPEs) 



FOSSORIAL 



(burrowing types) 



TERRESTRIO-AQUATIC 



(amphibious types) 



AQUATIC 



PALUSTRAL, LACUSTRINE 



(surface-living, bottom-livk 



FLUVIATILE 



(fresh-water, swift current, slow- 

 current; fluvio-marine types) 



MARINE LITTORAL 



(surface- living and burrowing types) 



marine pelagic 



(free surface-living, drifting, float- 

 ing, self-propelling types) 



marine abyssal 



(deep bottom-living types, slow- and 

 swift-moving) 



Each of the chief habitat zones may be divided 

 into many subzones. The vertebrates may mi- 

 grate from one to another of these habitats, or 

 through geophysical changes the environments 

 themselves may migrate. Conditions of locomo- 

 tion result in forms that are quadrupedal, bipedal, 

 pinnipedal, apodal, etc. 



