8 A BOOK OR WHALES 



the muscles of the trunk. These run in all directions, 

 and so account for the varied movements of the 



organ. 



There are diverse opinions as to the nature of the 

 whale's tail. The late Dr. Gray was strongly of 

 opinion, as are or were some others, that this organ 

 is to be looked upon as the degenerate equivalent 

 of the posterior pair of limbs. 



It must be admitted that there is a prima facie 

 possibility in favour of this view, which is not un- 

 attractive. We should have on this hypothesis the 

 whales exhibiting the last term of a series commenced 

 by the sea-lions. It has been also pointed out that 

 the backwardly-directed rudiments of the bony hind 

 limbs conform to such a way of regarding the matter. 

 It seems as if they had shrunk while the folds of 

 the integument originally connected with them had 

 remained, forming the flukes. There are not wanting 

 analogies to support this theory. It is known, for 

 instance, that there are, as a rule, fewer rectrices 

 (tail feathers) in modern birds than in Arch&opteryx, 

 where each of the free caudal vertebrae supported a 

 pair of these strong feathers. In modern birds the 

 rectrices are all attached to the terminal ploughshare- 

 bone of the tail, which is produced by a fusion 

 of not more than six or seven vertebrae. Now 

 as there are occasionally more than six or seven 

 pairs of rectrices, it looks much as if the epidermal 

 structures had remained while the corresponding 

 skeletal structures had vanished. Again, to take an 

 example from a widely different class --there is a 



