A DEGENERATE GLAND. — PRINCE. 221 



merely a rudimentary trace of it in .some species, and if so 

 many Teleosteans have become bereft of this organ and now 

 show no traces of ever having possessed it, I see no impro- 

 bability in the view I now urge that the Ganoids and Dipnoans, 

 possessing a ventrally-placed lung-like sac, have acquired it as 

 a new development, a new organ, and that it, not the dorsally 

 connected swim-bladder of other fishes, is the prototype and 

 homologue of the lungs of higher Vertebrates. This organ, 

 arising de novo as it seems to me, was provided with a vascular 

 supply (a venous connection) quite different from that, an 

 essentiallj^ arterial one, which is exhibited by the swim-bladder 

 in most fishes. 



Regarding, then, the swim-bladder as primitively a gland 

 whose original use is gone, like so many disused organs in the 

 animal frame, can it be said that it has any use now, or have the 

 various functions attributed to it, hydrostatic, accoustie, 

 barometric, respiratory, &c., little or no basis in fact ? I 

 have already pointed out that nitrogen has been found by 

 physiologists associated in the living organism with a state of 

 dormancy and inanition, and with altered alimentation, i. e., a 

 change in the nature of the food. Both these states are charac- 

 teristic features in the life of fishes. Whether fish sleep or not 

 is a matter of controversy ; but that they may pass into a state 

 of dormancy, a condition of inanition, is well-known, while the 

 changes in the diet of fishes, at various ages in the young, and 

 at particular seasons in the adult fish, are recognized by all 

 authorities. The storage of nitrogen, secreted from the blood 

 circulating in the vascular network of the swim-bladder, may 

 be associated with either or both of these states, a state of 

 dormancy or inanition, or a state induced by a marked change 

 in the character of the nutriment or food consumed. In ven- 

 turing to interpret the swim-bladder as a glandular structure, 

 whose original function has gone, I have done so because that 

 interpretation best accords with its character in the embryonic 

 and larval condition of the fishes possessing it. To all the 



