The Swim Bladder of Fishes a Degenerate Gland. — By 

 Professor Edward E. Prince, F. R. S. Canada, 

 Dominion CorriTnissioner of Fisheries and Directorof 

 the Marine Biological Station of Canada, formerly 

 Professor of Zoology in the Medical College of Glasgow 

 Royal Infirmary. 



(Read 9th February, 1903.) 



On examining, after appropriate dissection, the abdominal 

 viscera of such a fish as a cod or herring, a prominent sac is 

 seen occupying a considerable space underneath the vertebral 

 column or rather underneath the kidneys and dorsal aorta (see 

 Plate 20, fig. 1, s. b.). In the herring this sac communicates, as 

 in most physostomous fishes, with the fore-portion of the alimen- 

 tary canal, really in this case the stomach (Plate 20, fig. 3, d.) 

 though as a rule with the cesophagus as in the carp (Plate 20, 

 fig. 2,). The canal may be closed, and in all physoclistous fishes 

 it wholly disappears. The perch (Plate 20, fig. 2), the haddock, 

 (Plate 20, fig. 1), the cod, mackerel, &c., exhibit no duct. 

 In some Teleosteans the swim-bladder is absent and in 

 certain sharks and dog-fishes it is represented merely by 

 a slight diverticulum in the dorsal wall of the gullet. The 

 swim-bladder is, however,^ of general occurrence amongst 

 osseous fishes, and its primitive character is proved by its mode 

 of origin as a direct pocket or evagination from the pharynx, 

 in the embryonic stages of fishes. The distinguished Scottish 

 anatomist, Professor John Cleland, indeed, expressed the view 

 that the parts of the digestive tract in fishes, so often difficult 

 to determine, may be, in part at any rate, decided by the point 

 at which tlie swim-bladder is pushed out. (See list of literature 

 referred to, Xo. 5). 



A glance at the extensive and scattered literature, dealing 

 with this interesting organ, shows that very diverse views are 



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