METABOLISM 299 



heat as possible is retained by the body. The venules first return the 

 blood to a rather sparse network in the dermis, and then carry it back 

 through the blubber. Another set of venules surrounds the arterioles very 

 much as ivy encircles a tree (Fig. 172). From the fact that Cetaceans have 

 only half as many papillae per square millimetre of skin as, for instance, 

 man, we may take it that, despite this elaborate vascular arrangement, 

 their skin contains relatively less blood than that of other mammals. 



In an eighty-nine-foot Blue Whale which tipped the scale aboard the 

 Hashidate Alaru at 136 -4 tons, the blubber was found to weigh twenty tons, 

 i.e. about 15 per cent of the animal's total weight. Actually, its blubber 

 must have been rather thin, for the normal percentages are: Blue Whale - 

 27 per cent. Fin Whale - 23 per cent, Sei Whale - 21 per cent, and Sperm 

 Whale - 32 per cent. In Right Whales, the corresponding figures are 

 36-45 per cent, and in dolphins 30-45 per cent. Porpoises, too, have a very 

 thick blubber ; that of a number of Danish specimens was found to repre- 

 sent 45 per cent of the total weight. Specimens from the North Sea are 

 usually leaner, though 60 per cent was measured in one case. The actual 

 thickness of the blubber varies from species to species, but is greatest in 

 Right Whales, and especially in Greenland Whales, whose blubber has an 

 average thickness of twenty inches and, according to Zenkovich (1956), 

 of twenty-eight inches in some parts. Sperm Whales and Humpback 

 Whales also have sizeable blubber coats with an average thickness of 

 five to seven inches. Fin Whales and Blue Whales have coats three inches 

 and six inches thick respectively, and Sei Whales very much thinner coats 

 still. Now, all these figures are only rough approximations because blubber 

 is by no means of even thickness throughout. In large Rorquals, for 

 instance, it is thickest on the dorsal side of the lumbar and caudal regions, 

 and thinnest on the flanks. Moreover, blubber increases in thickness from 

 the front to the back, so that the top and bottom of the tail are particularly 

 fat. Thickenings of blubber also occur on the upper side of the lower jaw, 

 in front of the blowhole, at the base of the pectoral fins, and just in front 

 of the dorsal fin. The blubber is particularly thin round the eyes and a 

 little to the side of the blowhole, which is probably connected with move- 

 ments of the eyelids and the walls of the blowhole. While the thickness of 

 the blubber varies from species to species, and from season to season, the 

 relative proportions of the blubber remain unchanged. In other words, 

 differences in blubber thickness from part to part do not depend on food 

 supplies but on streamlining, which is not so much the result of mere fat 

 as of the particular distribution of the fatty tissue, just as the details of our 

 own shape and physiognomy depend largely on the distribution of our 

 own subcutaneous fat. 



According to Heyerdahl (1932), the only scientist to have made a 



