WHALES 



413 



tion was once ascribed to their supposed value in keeping the eye warm, 

 the idea being that all of their contractive effort goes into heat; but this 

 theory is scouted by recent authorities. The loss of ocular rotability has 

 had no serious consequences in itself; for the whale eye, situated always 

 close to the angle of the jaws and thus as much as a third of the way 

 back along the body (where the head is that large — as it often is) , is quite 

 incapable of forward vision anyway, to say nothing of binocular cooper- 

 ation with its fellow. 



In many cetaceans, the immobility of the eye can be blamed upon 

 the enormously thick, stiff sheath of the optic nerve (Fig. 141). When 



Fig. 141- 



a, a mysticete, Balcenoptera physalis. X Vi; from 



b, an odontocete, Phocxna communis. xWi. 



Whale eyes. After Putter. 



72-foot individual. 



vv, vorticose vein. 



the eye is immobile, it is only natural that if some particular direction of 

 vision is most important, the eye should take on a permanent orientation 

 in that direction. We have seen this to be true in owls, prosimians, and 

 deep-sea fishes. For the whales, this most important direction appears to 

 be downward, and the eyeball is canted ventrally or nasoventrally, with 

 some internal asymmetry which helps out in tilting the visual axis. This 

 is a prima facie reason against supposing that the whales ever care to try 

 to see out of water. 



The eyelids have altered in sympathy with the ventrad torsion of the 

 globe. In the odontocetes they are quite equal, for the upper and lower 

 culs-de-sac have together been shifted to equal extents around the eye in 



