EVOLUTION AND EXTERNAL APPEARANCE 



Figure 41. The shape of different Cetaeea, seen from below. Umbilieus and anal aperture 

 have been ringed. From left to right : Sei Whale, Sperm Whale, Beaked Whale, Pilot Whale, 

 Porpoise. Note the differences in shape of head and tail, and in pectoral fin attachment. 

 Note also that maximum girth need not coincide with ma.ximum breadth, since girth is largely 



determined by height. 



For almost a hundred years, scientists have vainly tried to discover the 

 significance of the grooves. Lillie, one of the greatest experts on Cetaceans, 

 who lived in the nineteenth century, showed that the grooves made 

 possible local expansion of the skin. This is quite apparent in recently 

 killed whales. Whenever air is pumped into them, or when putrefaction 

 has set in, the caixasses become so distended that the folds disappear 

 completely and the skin beneath the snout and chest looks like a gigantic 

 blown-up balloon. Lillie thought that this elasticity enabled Rorquals 

 to increase the capacity of their mouths and to swallow the enormous 

 quantities of krill (see page 255) on which they feed. This might explain 

 why Right Whales have no grooves - their strongly arched jaws provide 

 adequate space as it is, and their feeding habits differ radically from those 

 of Rorquals (cf. Chapter 10). However, none of these explanations really 

 tells us why the grooves run so far back. Possibly, long grooves obviate 

 undesirable skin tensions or else they have some part to play in breathing. 

 We shall see later that Rorquals have a very large diaphragm and that 

 abdominal breathing plays an important part in their respiration. The 

 grooves might very well help the expansion of the otherwise rigid skin. 



Other biologists believe they have found a connexion between the 

 grooves and the aniinals' speed. Smooth whales are always slow swimmers, 

 while most Rorquals can develop great speeds. The grooves might well 

 serve to remove hydrodynamic friction, and thus provide better water 



