ANIMALS THAT LIVE WITHOUT WATER 163 



(Phoca barbata and P. foetidu), give no evidence that 

 these animals have superior renal concentrating power 

 or that they can drink sea water, while calculations based 

 on the composition of the diet indicate that they can 

 live on the free and metabolic water of their food. The 

 seals, porpoises, and dolphins eat mainly fish, the killer 

 whale eats the flesh of other whales, birds, and seals; 

 the bottle-nosed whale and sperm whale eat cuttlefish 

 and squid. The whalebone whale (including Balaenop- 

 tera) lives on plankton (small animals) and fish which 

 it collects by straining sea water through its mouth where 

 the plankton is caught on the blades of whalebone hang- 

 ing from the palate. There may be as many as three 

 hundred or more of these blades on each side, and those 

 in the middle may reach a length of lo to 12 feet. At 

 the inner edge they fray out into long, delicate, but 

 tough hairs, and their arrangement is such that they fold 

 back when the mouth is shut, but unfold and completely 

 fill the cavity when the mouth is open, so that all the 

 animal has to do is to open and close the mouth in order 

 to filter out from one to 50 gallons of small organisms. 

 When the mouth is closed the tongue is forced against 

 the palate, expelling most of the water and concentrat- 

 ing the filtered food into a semisohd mass which ap- 

 parently is well compressed before swallowing, since the 

 urine gives no evidence that the animal takes in much 

 sea water. 



The harbor seal, Phoca vitulina, is the only one of the 

 marine mammals that has been studied in detail. This is 

 a strictly marine form that feeds on fish that it can swal- 

 low either above or below the water; in the latter in- 

 stance the esophagus wipes the fish virtually dry as it 

 goes down. The seal opens its mouth frequently under 

 water, and sometimes plays with a fish for a long time 

 before swallowing it— mouthing it, letting it loose and 

 mouthing it again— but at no time does it swallow any 

 significant quantity of sea water. 



