1874.] SPECIES OF EUPHYSETES. 263 



guished by the nostrils being enormously disproportionate in size, 

 the left one being the largest ; at the same time the nasal bones, as 

 those of the face, are generally unsymmetrical and distorted. 



Of them, the genus Euphysetes may be said to possess this un- 

 symmetrical distortion of the skull and the difference in the size of 

 the nostrils in the highest degree. 



Systematic zoologists have generally hitherto had little time to do 

 more than to fix the so-called generic and specific characters, without 

 being able to examine into the causes why certain animals exhibit 

 such peculiar forms and 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 develop them to a more or less degree, or stunt their 

 growth, 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 {Strigops habroptilus) has also altered 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 symmetry of the skeleton is not interfered with. 



In some other cases (as, for instance, in the Pleuronectidae or flat- 

 fishes) 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 doubtless have 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 appear to exist ; 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 pulmonary vapour to be expelled found the 

 same amount of room for passing to and fro. Thus in the skull of 

 the Epiodon chathamiensis 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 intermaxillary bone being far more developed than the left 

 one, and, moreover, rising as a broad ridge to the very summit of 



