468 ANNUAL REPORT SMITHSONIAlSr INSTITUTION, 192 8 



The possibilities for wide dispersal of cetaceans are exceptionally 

 great, in view of the absence of physical barriers, and apparently 

 the chief controlling factor is the food supply. Hence it may appear 

 rather surprising that some of the larger whales, such as the gray 

 whale, the humpback, and the bowhead, should follow definite routes 

 in their migrations. The kind of plankton eaten by whalebone 

 whales, according to Bigelow (1926, p. 99), is lai'gely determined by 

 the fineness of their straining apparatus. This consists of a row 

 of contiguous blades of baleen hanging downward from the roof of 

 the mouth on each side. These blades of baleen have internal mar- 

 ginal fringes of intcrmatted bristlelike fibers which function as a 

 sieve when the animal is feeding and thus prevent the egress of 

 plankton too large to pass through the interspaces with the outi'ush 

 of water when the mouth is closed. Mysticctes with coarse coml>like 

 Avhalebone, such as the finback, the blue whale, and the humpback, 

 can capture the large euphausids, but the smaller calanids escape 

 with the outpouring water. The unusually fine bristles of the sei 

 whale and the North Atlantic right whale sift out the smaller calanid 

 copepods as well as the larger shrimplike euphausids. But whales 

 with coarse-fringed whalebone seem to be much more adept in cap- 

 turing fish than those with fine-fringed whalebone. 



Some of the whalebone whales consume enormous quantities of 

 these euphausids, and on the Antarctic whaling grounds most of 

 them feed almost exclusively upon these minute crustaceans. Even 

 the blue whale, the largest mammal that has ever lived, seems to be 

 dependent upon such small prey. Prof. G. O. Sars found that the 

 stomach contents of a blue whale taken in the Norwegian Sea con- 

 sisted chiefly of a small shrimplike crustacean {Thysanoessa in- 

 ermis), and Collett (1877, p. 161) reports that occasionally one is 

 taken that has eaten nearly 1,200 liters of Thysanoessa. The shrimp- 

 like Thysanoessa and Meganyctiphanes in the North Atlantic and 

 Euphausia in the Antarctic seem to constitute the bulk of the food 

 of the blue whale. The food of finbacks may vary according to local 

 conditions, for the stomach of one (Cornwall, 1928, p. 11) taken 

 near Vancouver Island was filled with a small squid {Gonatus fah- 

 rici). Morch (1911, p. 066) has pointed out that the distribution of 

 finbacks in the North Atlantic depends upon the seasonal appearance 

 of plankton, capelan {MalJotus viJJosus), and herrings. Bryde's 

 whale {Balcenoftera hrydei) does not seem to be wholly dependent 

 upon the occurrence of euphausids according to Olsen (1913, p. 

 1085), as it is generally seen near the shore feeding on fish, such as 

 herring and mackerel, but in one instance sharks over 2 feet in length 

 were found in a stomach, and in another case no less than 15 pen- 

 guins {Spheniscus demersus) and " malagass " {SuJa capensis). The 

 same writer states that copepods (Calanidse) are the chief source of 



