1 6 A BOOK OF- WHALES 



THE PECTORAL FIN 



The flippers of the whale correspond of course 

 to the anterior pair of limbs in other vertebrates. 

 Whales have only the rudiments of posterior ap- 

 pendages. The limbs vary much in length and 

 shape, being sometimes rounder and sometimes 

 longer and narrower. The tip may or may not be 

 curved round the appendage, in the former case 

 acquiring a falcate form. The limbs of whales do 

 not seem to be much used for progression. They 

 are rather used as balancers, and thus resemble the 

 anterior fins of fishes. Scoresby studied the action 

 of the fins through a telescope, and came to the 

 conclusion that they were balancers ; and besides, 

 when a whale is dead it heels over on to the side, 

 a fact which seems to be a further proof that this 

 is the function of the flippers. 



The superficial likeness of the whale's flippers to 

 the fish fin has been mentioned. It is exceedingly 

 interesting to find that there are deeper seated 

 likenesses ; these are of course coupled with essential 

 similarities to the hand of the mammalia ; and by 

 comparing the two series of facts with each other, 

 and with facts derived from the study of other aquatic 

 creatures, such as the seals on the one hand and 

 aquatic reptiles, such as Ichthyosaurus, on the other, 

 it seems possible to extricate characters that are due 

 to the aquatic mode of life. 



It will be necessary, however, to preface the 

 description of the actual facts in the structure of 



