47 



insulated afgainst the loassage of heat, as by the fur of mammalR, the 

 feathers of birds. From the need of such thermal adaptations marine 

 life is freed, because the changes in tet-iperature at any given place 

 in the sea average not only very much smaller than they do in the 

 air, but very much slower. Throughout the niost of the ocean deeps, 

 in fact, the temperature is practically unvarying from year's end 

 to year's end. And while shoal waters in high latitudes do show 

 considerable alterations, in this respect, with the change of the 

 seasons, it is only close to the surface that such changes are 

 great. And even there any cinimal can reach a nearly constant 

 thermal environm.ent by merely swimming down a few fathoms to avoid 

 extremes of summer heat or of winter cold, as many fishes actually 

 do in their regular bathic migrations. 



On the whole, therefore, marine animals have not found it 

 necessary to provide any specific protection against variations in 

 temperature. 'The general rule in the sea is that the temperature 

 of any animal is practically that of its surrounding water, rising 

 or falling as the latter rises or falls. This, it is true, also 

 applies to cold-blooded animals on lo,nd. But whereas the latter 

 pass through alternating periods of activity and of stagnation 

 everywhere except in the Tropics, no such rule governs in the sec, 

 each species being attuned to a certain optimum range within which 

 it pas.:es most of its life, but within which range various phJ-ses 

 of its vital rctivities, cspecia.Ily of i"!;s reproduction, are iir- 

 ectly controlled by the teiTiperature. Otherwise expressed, cold- 

 water xiGhoG i-xiy be quite as active as warm — witness the trouts and 

 salmons. When, as soretimes happens, a sudden fatal shift in the 

 temperature onuses widespread destruction ( Page 7C ) , nature's only 

 provision for the re^^stablishraent of the species in the sea i3 by 

 the production of many .^ore eggs and young than can survive under 

 normal conditions. But both the metabolic activity and the theri::- 

 odynamic efficiency of the organism as a whole are far lower in cold 

 blooded tJvin iji warm blooded animals. This suggests a field d:c en- 

 deavor of great interest. 



The discovery of warm blood has never been irade in the 3.^a. On 

 the contrary, all the warm-blooded animn.ls that now inhabit the sea, 

 whales, seals, walrus, etc., are descended from warm-blooded ter- 

 restrial ancestors. To maintain a high body temperature demands 

 more rinid oxidization within the body, and more food. Thus, not 

 only is it no advantage in the sea, but it is a positive handicfp 

 there, because; the high thermal capacity of the surrounding water 

 malces the maintenance of self-controlled temporaturc miUch more dif- 

 ficult than it is in the air, for cold water ttilces much heat fror 

 any warmer body before its own temperature rises equally. A fami- 

 liar example cf this is the use of water in the cooling systo.ns_ of 

 automobiles. It is to meet this oroblem. of insulation that i/vialcs 

 and seals are enclosed in a layer of blubber. But this blubber 

 means added bulk; bull: not of direct service, except as protection 

 against outside influences, but actually detrimental because itu, 

 presence ma'res it more difficult to tjropel the body through the 

 water; because, too, its maint'?nance requires more food. Contrast 

 with this the happy condition of the fish for which fat is not need- 

 ed at all for the ourpose of insulation, but serves purely as a 

 storehouse for energy that can be drawn on even to the noint of to- 

 tal exhaustion whenever f. amine may require it. 



