27 



those of marine habits for an evident purpose, and that purpose must be 

 an increased susceptibility to external sounds beyond those in their native 

 element. 



As to the position of the otoliths within the skull iu a state of 

 nature, it is difficult for one without anatomical knowledge to speak 

 positively ; but by an inspection of carefully dried heads, I am inclined to 

 think they are almost invariably suspended lengthways and edgeways, 

 in a horizontal, but somewhat leaning position. In the majority of 

 instances the larger end of the otolith is directed forwards, but there are 

 many cases in which this is reversed. Ko two species of fishes have them 

 identical in shape even when closely allied, and the difference is often 

 particularly marked in those examples most nearly related to one 

 another, thus it is claimed that a knowledge of the/ie bones will afford a very 

 reliable subsidiary test for the discrimination of species. 



It is, of course, impossible to point to the otoliths of any particular 

 fish as types, or to describe specimens in any progressional order, but as 

 those of the cod ( Gadus morrhua) are known to many who have seen no 

 others, it will be convenient to start with this fish. 



The first three figures on the accompanying plate, show in outline, 

 (natural size) the form of this fishes otoliths, and the first thing we notice 

 is, that notwithstanding the growth of the fish from the immature 

 codling of a total length of fourteen inches, to the deep-sea adult with a 

 head alone of upwaids of nine inches, there is but little relative difference 

 in the size of these bones superficially. Age gives breadth and thickness, 

 but scarcely adds anything to the length of the otolith, whilst the larger 

 end becomes more truncate, and the wrinkling disappears in a great 

 measure; the obtusely toothed edges too, are no longer so prominent, but 

 the longitudinal fissure is deeper and broader. It must not be assumed 

 from this change that the fish, like an old countryman, becomes " hard of 

 hearing," but rather that this unevenness of surface is not given like our 

 outward ear for a gathering of sounds, so much as for the attachment 

 of the nerves, and therefore, no longer required when the fissure is 

 deepened. It cannot be that more acute hearing power is required by 

 the young in shallow waters, than when as larger fishes they go to 

 greater depths, because if this were so we shoulcl find the same fact to 

 hold good with other species, and this is not the case. We further 

 see that the difference between the sexes is markedly shown, the broader 

 and shoi'ter otoliths always belonging to the female fishes. 



Prom the codfish to the haddock {Gadus ceglefinus) is but a step, 

 but a very different style of otolith awaits us. Its position in the skull 

 is the same as the cod, and like that fish, the broader end points forward, 

 but there the similarity ceases. The sides are parallel instead of uniformly 

 swelling outwards, the rugosities have almost disappeared, and the teeth 

 along the edge of the lower side are more regular and very much slighter, 

 the upper end is abruptly slanted off, and the opposite extremity obtusely 

 pointed. There is no perceptible difference in the otoliths as the fish 

 gets older. 



