A DEGENERATE GLAND. — PRINCE. 205 



(Coregoni), the grayling (ThymaUus), the shallow-water Gastro- 

 steida3 and the river-ascending salmon, none of which seem to 

 need any such supposed potent help to give them floating power. 

 On the other hand, in the sea bass it is small, and in all the 

 Serranid^ it is adherent to the abdominal walls. No fishes 

 apparently need this organ less than the fresh- water suckers, 

 yet without exception the Moxostomida? and Catastomida^, 

 pfrovellino; on the bottom of rivers and lakes, have a swim- 

 bladder, consisting of two or three large sacs. To fish like the 

 cod and certain deep-water lake whitefishes. it appears not only 

 useless to aid them in rising in . the water : but may even be 

 fatal to them for when brought up from the bottom the 

 expanded swim-bladder may seriously disorganize the fish and 

 force the abdominal viscera out of the mouth. The halibut and 

 flat-fishes can rise in the water, though these fish, so much in 

 need of such an instrviment of buoyancy, are not provided with 

 it : neither are the Scombridse (with such exceptions as Scomber 

 jctponicvs as already pointed out) although to quote Mr. 

 Boulenger (No. 1, p. 65) this family are " unceasingly active, 

 their power of endurance in swimming being equal to the 

 rapidity of their motions." The Cottidae or Gurnard family 

 have a well-developed swim-bladder yet, as the authority just 

 quoted says, they are " bad swimmers and generally living at 

 the bottom near the coasts" (No. 1, p. 62) — ^just as the 

 Polynemida? have a large swim-bladder, yet are purely littoral 

 fishes, frequently hovering about the estuaries of rivers. The 

 immortal Baron Cuvier, struck by the erratic occurrence of this 

 supposed buoyant provision, admitted th t he saw no 

 meaning in it and was unable to understand the want of so 

 large an organ, not only in fishes wdiich frequent the bottom, 

 like skates and flat-fishes, but in many others which apparently, 

 he said, were second to none in their rapidity and their facility 

 of movement, such as the mackerel. 



Its position immediately beliind the cephalic or branchial 

 section of the alimentary tract and its communication by an 



