572 Dr. Michael Grabham [May 5 



Sebastes, which live in equally deep water, though seldom in close 

 association with their leaden-coloured brethren. No one, however, 

 who has not assisted at the capture of these abysmal inhabitants can 

 have any true idea of the gorgeous tints of the dullest of these 

 creatures on first emerging from the sea. 



The sherny has a very large bladder firmly attached to the spine, 

 and a few words on the nature and use of the air-bladder generally 

 will not be out of place here. The function of this organ is as yet 

 by no means clearly made out. You will read of them as swiin- 

 1 (ladders, especially as relating to the carp and other fishes frequenting 

 superficial waters, which are believed to regulate their submersibility 

 by a voluntary act of filling, compressing or emptying the bladder of 

 its contained gas. But the physiology of the organ is by no means 

 so simple as this. It varies much in size. Here it is large, but in 

 the Aplurus, or oil fish, which lives in company with it and feeds on 

 the ocean floor, it is completely absent. The air-vessel has, indeed, 

 in many cases a pervious duct opening into the intestinal canal, but 

 the duct is often absent altogether or obliterated into a solid cord in 

 the full-grown fish, leaving the bladder a closed sack. The bladder- 

 walls truly contain muscular tissue adequate to the compression or 

 expulsion of the gas if there is a hollow duct and exit, but as the 

 vessel can only be again distended and filled by the gradual secretion 

 of gas from the blood, we may fairly assume that the voluntary 

 regulation of the specific gravity of the fish is, to say the most, a 

 subordinate portion of the bladder functions. On the other hand, 

 the extremely vascular development of the lining membrane into a 

 lung-like anatomy points clearly to pulmonary functions, and it is 

 quite likely that an interchange of gases may take place between the 

 two kinds of blood traversing the retia mirabilia in many fishes. 

 Moreover, and thirdly, in regard to the physiological functions of the 

 air-bladder, the position of the viscus, its firm attachment to the 

 spinal bones, and its prolongation upwards to connect in some 

 examples through a chain of ossicles with the organ of hearing, seem 

 a sure indication of the use of the organ as a resonator in the convey- 

 ance of sonorous vibrations to the auditory focus. The gaseous 

 contents of an air-bladder vary considerably, consisting mainly of 

 nitrogen in many instances. But after examining the bladder of 

 eighteen large examples, presumably from very deep water, during the 

 last few weeks, I am unable to confirm the current idea that the 

 viscus is charged with oxygen in the abysmal depths ; nor is it 

 probable that a fish could afford to secrete or excrete a gas so vital to 

 its welfare. 



Speaking generally, the consumption of oxygen by fishes is 

 comparatively small, especially in regard to tribes inhabiting stagnant 

 waters — a man, for instance, absorbing many thousand times the 

 amount required by a tench. But with the active Scromiidse the 

 requirement is of course greater, and the fish has often a higher 

 temperature than the water in which it swims. 



