314 WHALES 



fact. Fetcher's and other scientists' experiments tell us little on this subject, 

 and all we really have to go by is the size and structure of the kidneys. 



The ratio of kidney to body weight was found to be o -44 per cent in two 

 Fin Whales, 0-5 in a Humpback Whale, i-i per cent in a Bottlenose 

 Dolphin and a White-sided Dolphin, and 0-84 per cent in several por- 

 poises. While a number of biologists have shown that, with increasing 

 body weight, there is a decrease in the kidney-to-body-weight ratio, 

 comparisons between porpoises and dolphins on the one hand and human 

 beings (0-37 per cent), zebras (0-4 per cent) and a number of deer 

 (0-35 per cent) on the other, or between Rorquals and elephants (0-29 per 

 cent) show clearly that the relative weight of the Cetacean kidney is 

 exceptionally large. 



The Cetacean kidneys are found in the same place as they occupy in 

 terrestrial mammals: on the dorsal wall of the abdominal cavity. They are 

 two long, fairly flat and rather broad organs and are surrounded by an 

 outer cortex consisting of connective tissue. From the shape of the cortex 

 alone, we can tell that Cetacean kidneys are divided into a large number 

 of small lobes, called renculi, and thus resemble the calves' kidneys which 

 we buy at the butcher's (Fig. 175). However, the number of such renculi 

 is very much larger in Cetaceans than it is in cattle. Thus the Finless Black 

 Porpoise {Neomeris phocaenoides ; length 4I feet) has 150 per kidney, the 

 Common Porpoise 250-300, dolphins about 450, Belugas about 400, and 

 Rorquals about 3,000. Every renculus is really a complete kidney with a 

 cortex, a medulla, a papilla and a calyx of its own. Occasionally, two or 

 more of the lobules become fused, and generally 4-6 of them have a 

 common duct to the ureter which collects all the ducts of all the renculi 

 and finally leaves the kidney on its caudal side. The fine structure and the 

 circulation of the Cetacean kidney do not differ significantly from those 

 of other mammals, some of which also have lobular kidneys instead of the 

 smooth kidneys of man and horses. Lobulated kidneys are found not only 

 in cattle (which have twenty-five to thirty renculi) but also in the rhino- 

 ceros, in otters, bears, elephants (eight renculi), seals, sea-lions and sea- 

 cows (see Fig. 175). The dugong, on the other hand, has a smooth kidney. 



In seals, the number of lobules is almost as large as in Cetaceans. Now, 

 the greater the number of lobules, the larger the cortex and, since it is in 

 the cortex that saline is removed from the bloodstream, the greater the 

 excretion of urine (it is not quite clear what precisely happens in the 

 medulla, but it seems likely that at least part of the water is returned to 

 the bloodstream here). In animals which excrete a great deal of urine 

 with a salt concentration equal to that of the blood we must therefore 

 expect a strong increase in the cortex, which in turn is evidence that a 

 great deal of urine is being excreted. 



