Haast. — On Euphysetes pottsii. 101 



colours, and why their skeletons have assumed the distinct morphological 

 characteristics by which they are distinguished from all others. 



We can understand that the use or disuse of certain limbs of an organism 

 may develope them to a more or less degree, or stunt their growth, and by 

 which other portions of the skeleton will in their turn become differentiated. 



Thus, to give only one instance, the disuse of the wings of the Kakapo 

 (Stringops habropiihis) has also altei'ed the form of the sternum, which has such 

 a very prominent keel in the whole Parrot tribe, to such an extent that it is 

 only feebly marked ; but in this case, as in most others, the symmetiy of the 

 skeleton is not interfered with. 



In some other cases, as for instance in the Pleuronectidce, or Flatfishes, we 

 can easily trace the asymmetry of their skeleton to adaptation, viz. : to their 

 mode of obtaining food, and at the same time preserving themselves from their 

 enemies. If, in the struggle for existence, they had not, in the course of ages, 

 assumed their present form they would have doubtless long become extinct. 

 Moreover, we know that the Flatfishes are symmetrical in the young state, 

 and as they grow older the skull not only becomes distorted, but one eye 

 actually crosses gradually from one side to the other to take its place close to 

 the other eye. 



However, in the instance of the toothed whales, at least at first sight, such 

 vital considerations do not apjDear to exist, as the blow-holes, or naso-palatine 

 breathing passages, situated on the very top of the head — by which the 

 Cetaceans have to expose only a very small portion of their body when they 

 rise to the surface for expelling the pulmonary discharge of used-up air, by 

 which the spout is generally formed, and for oxygenizing again the blood by 

 inhaling a great quantity of atmospheric air — do not receive more protection 

 by being so remarkably unequal in size. Moreover, it appears to me that an 

 animal would breathe as freely and effectually if the blow-holes were of equal 

 size, of course always provided that the quantity of air to be inhaled, and of 

 the pulmonaiy vapour to be expelled, found the same amount of room for 

 passing to and fro. Thus, in the skull of the Epiodon chaihamiensis— described 

 by Hector,* and of which we possess a fine skeleton in the Museum — the blow- 

 holes, although twisted considerably to the left, are of the same size ; but the 

 asymmetry of the upper portion of the skull is produced by the right inter- 

 maxillary bone being far more developed than the left one, and, moreover, 

 rising as a broad ridge to the very summit of the skull, and forming there a 

 crest of considerable size on the right side only. 



Unfortunately I have not access to all the necessary works of reference to 

 enquire if this qiiestion — as to causes, growth, and uses of asymmetry in the 

 toothed whales— has already been treated by naturalists in the northern 

 * Trans. N.Z. Inst., Vol. V., p. 164. 



