172 WHALES 



connexion, he studied the regulation of heat losses, particularly in aquatic 

 mammals. He was struck by the fact that the pectoral fins and the flukes 

 are only provided with a thin layer of insulating blubber, and that, 

 therefore, considerable heat losses must occur in these regions. In fact, 

 measurements revealed that the pelvic flippers of seals and the flukes of 

 porpoises were at water temperature, while the temperature of the rest 

 of the body was at least 1 5 degrees higher. The fins and flukes would thus 

 act like pumps drawing heat from the rest of the body, were it not that the 

 retia prevented them from doing so. In the retia, the warm blood going to, 

 and the cold blood returning from, the flippers and flukes are brought 

 into close contact, and an exchange of heat is effected between them. Thus 

 the arterial blood warms the venous blood returning from the extremities, 

 while all the arterial blood that reaches them has first been cooled by the 

 veins. 



It is also possible that under certain conditions, such as great muscular 

 exertion, the body may become overheated. While men can get rid of 

 surplus heat by sweating, Cetaceans have no sweat glands and moreover 

 are surrounded with thick layers of insulating blubber. Hence the excess 

 heat must be lost in a diflferent way, i.e. through the flippers and flukes. 

 Tomilin, investigating an East Siberian Dolphin, found that the tempera- 

 ture of the fins varied by as much as 13-5° C or 24-3° F (20° 0-33-5° ^)j 

 while the temperature of the rest of the body fluctuated over a maximum 

 range of 0-5° C. Schevill, working in a warmer climate (Florida), found 

 that the temperature of the fins of a Bottlenose Dolphin was 10° C above 

 that of the rest of the integument. Scholander assumes that, during over- 

 heating, the circulation in the tail is so regulated that the blood returning 

 from the flukes does not pass through the retia but mainly through the 

 lateral veins of the tail. The arterial blood therefore retains its heat until 

 it reaches the flukes, there to lose it to the sea. Whether similar processes 

 also occur in the flippers still needs to be investigated by careful anatomical 

 examination. It must, however, be mentioned that heat losses are also 

 controlled by similar mechanisms in the entire integument of all Cetaceans 

 (see Chapter 11), and that this type of retia mirabilia is also found in 

 sea-cows. Sea-lions and seals, however, do not have them. The only 

 exception is the walrus which has extensive retia in the lower fore and 

 hind limbs. Retia also occur in some terrestrial mammals such as sloths, 

 ant-eaters, and some lemius, in all of which they have a clear heat- 

 regulating function. 



It goes without saying that many scientists who study the blood of 

 Cetaceans do so in the hope of probing some of the mysteries of mam- 

 malian life under water. Now, while there is never any shortage of such 



