46 



carried from place to place. Thus the dissemination of whole groups 

 of species is assured in the sea v/ithout directive swiuuning on tneir 

 own part. And even the fishes benefit thereby in their egg and 

 larval Gtae;es - or suffer if carried into unfavorable surroundings. 



Thus, while it is true that nany groups of animals in tho sea 

 have been controlled in their stractural evolution, and in the 

 development of their appendages, by adaptations for locoruotion, such 

 as stream-lined body- forms easy to drive through the water, many 

 others arc free from this factor in form regulation. The latter 

 teach us, for example, that the possession of lateral limbs of any 

 sort, or of the bilateral sym;r.etry with which we are so familiar 

 that we have almost come to loolc on them as a necessary feature of 

 an animal, are actually not a basic necessity at all, but merely 

 adaptations to a particular environment, or way of life. 



The morphological simplicity of the many marine animals, even 

 some comparatively high in the scale, that are freed from the 

 necessity of this particular control, frees, in the sea, the 3tudy 

 of the basic relation of animal to environment from much of tho con- 

 fusion that puzzles the terrestrial ecologist. 



Corresponding simplicity in the internal metabolism of marine 

 animals is associated with the thermal character of the medium in 

 which they live. The more obvious of the complex ways that this 

 factor advantages the oceanic biologist, as contrasted v/ith his con- 

 frere on land, are as follows:- 



Living surrounded by air, the thermal capacity of which is^^so 

 low that it changes temperature very rapidly, and through a wide 

 range of variation with changes in the thermal determinants 

 (strength of the sun, direction of the wind, etc.), terrestrial 

 plants and animals must, by and large, be able to accommodate them- 

 selves to v;ide variations in tem.perature, or else be able to guard 

 themselves against the latter. Yi/ith temperature controlling the 

 rate of many chemical reactions, the activities of any animal liv- 

 ing where the tem.perature range is wide from hour to hour, from day 

 to day, or from season to season, are greatly limited if its own 

 body t9m.perature be the sam.e as that of the surrounding air; still 

 more so if its surface be pervious to direct solar radiation. A 

 familiar example of this law is the sluggishness of snakes, turtles, 

 etc., and of many insects, in cold v^eather, contrasted with their 

 activity in warm. The only method that nature has yet evolved, by 

 which animals can free themselves from this limitation of their 

 vital activities by changes in the temperature of their surroundings, 

 is by maintaining within their own bodies a comparatively constant 

 temperature: i.e., by the invention of "warm blood." Contrast, for 

 example, the efficiency as a vital machine, and the freedom from 

 seasonal pulses in activity, of one of the higher mammals with the 

 snake which, in high latitudes, must lie dormant half the year. 



While the maintenance of a self-controlled body tem.perature 

 does not require any general modification of the gross internal 

 anatomy, it does involve r.ietabolic adjustments so delicate that any 

 disturbance of the regularity of the control is apt to be fatal. 

 It also requires that the surface of the body be in some v/ay 



