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Show 1874.] S P E C I E S O F E U P H Y S E T E S. 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 unsymmetrical 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. W e 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 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 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 m e 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 |