EVOLUTION AND EXTERNAL APPEARANCE 9I 





Figure ^g. Whale lice in a groove on the skin {old scar) of a Rorqual. Prep : 11'. H. E. van 

 Dijk; Photograph : W. L. van Utrecht, Amsterdam. 



friction (Fig. 49). They are found abundantly in these shts on dead 

 whales. 



When we examine dead whales, we are struck by the fact that some are 

 more infested with lice and other parasites than others. Parasites are most 

 common in Right Whales - a Greenland Whale may have hundreds of 

 thousands of whale lice. Humpbacks and Sperm Whales also play hosts 

 to a multitude of unwelcome visitors, and Zenkovich mentions the case 

 of a Humpback carrying over 1,000 lb. of Acorn Barnacles and Stalked 

 Barnacles. Quite likely, the guests prefer these whales because they swim 

 more slowly than other Mysticetes. Among Odontocetes, not only Sperm 

 Whales, but also Bottlenose Whales, Pilot Whales, Killer Whales, Nar- 

 whals, Belugas and even Common Dolphins, are known to be infested, 

 while Common Porpoises and Bottlenose and many other dolphins seem 

 to be free of parasites. Of course, a more thorough investigation may reveal 

 external parasites on these species as well, but only in exceptional cases. 

 Even among infested whales, there ai^e marked individual differences, so 

 that we can distinguish between 'clean' and 'dirty' aniinals, though the 

 causes of this distinction are not yet understood. In terrestrial animals, 

 particularly of the domestic kind, such differences are often the result of 



