SOME INTERNAL STRUCTURES 49 



even been suggested that the peculiarity was originally 

 a pathological state of affairs caused by injury, and 

 that a one-sided face has been the consequent inheri- 

 tance. One associates symmetry with vertebrate 

 animals, and so especially with aquatic ones swimming 

 head foremost through the water that symmetry would 

 seem to be their most necessary attribute. It must 

 be borne in mine!, however, that the asymmetry is not 

 nearly so apparent in the head when clothed with 

 flesh. But the Sperm whale is markedly asymmetrical 

 in the single S-shaped blow hole. 



This absence of symmetry in the skull affects 

 especially the pre-maxillse and the nasals. The latter, 

 indeed, are often reduced to a single very small bone. 

 There is one toothed whale in which the asymmetry 

 of the skull is not so hard to understand, -that is, 

 of course, the Narwhal with its one rarely two 

 "tusk" projecting in front. This one-sided develop- 

 ment could be readily imagined as having affected 

 to a considerable degree the neighbouring parts of the 

 skull. But we cannot assume that other toothed 

 whales are the offspring of narwhal-like forms, though 

 it is certainly true that the narwhal is in some respects 

 a primitive whale. It is easier to say that the asym- 

 metry, being, as it is, chiefly developed in the regions 

 of the blow holes, has something to do with those 

 structures, than to find any adequate reason for con- 

 necting the two.* 



* Of course the unsymmetrical head of the flat-fish is not in any way 

 comparable ; in those fishes it is related to the fact that the sides of the 

 body are used as dorsal and ventral surface respectively. 



