A DEGENERATE GLAND. — PRINCE. 209 



supplant the mesenteric artery which supplies the organ in most 

 lislies and that the blood leaving the swim-bladder should go 

 direct to the heart rather than to the portal vein. In Ceratodus 

 (a case of exceptional significance) the arteriu coeliaca supplies 

 the swim-bladder, and the duct of the swim-bladder exhibits a 

 glottis.* True lungs, we know, arise as paired buds from the 

 ventral surface of the oesophagus (Plate 21, fig. 3), and it is 

 questionable to regard them as homologous with a dorsal diver- 

 ticulum such as the swim-bladder of fishes (Plate 21, figs. 1 and 

 2). They may be, and probably are, structures arising de novo- 

 May not this also be true of the lung of the Dipnoan fishes, as 

 the swim -bladder and its connecting duct may disappear, and 

 have done so completely in many fishes ? 



Closely connected with the supposed pulmonary character of 

 the swim-bladder is the theory that it is an aid in sound-produc- 

 tion. A hollow vesicle filled with gas may act as a resonator. We 

 know that in certain fishes sounds are produced. Thus, as Dr. C. 

 C. Abbott pointed out, the mud sunfish ( Acanthardtus ijomotis) 

 makes a grunting sound, the gizzard shad (Dorosor)ia cepedia- 

 niim) a whirring sound : the chub-sucker (Eritnyzon sucetta) 

 utters a prolonged note due, ic is said, to the air forcibly driven 

 through the duct of the swim-bladder, the cat-fish ( Ameiurus ) 

 hums softlj^ the '• Drums," like Aplodinotiis grunniens, make 

 a grunting or croaking noise, and such species of the Sciaenidaj, 

 as Pogonias make a loud drumming sound, especially loud in 

 the male fish, while the eel (Anguilla) is declared to utter a 

 musical note of a distinctly metallic character, These sounds, 

 says Dr. S. A. Packard, are homologous with those of reptiles, 

 birds, and mammals, being produced by the swim-bladder, which 

 that authority holds to be the homologue of the lungs. Dr. W. 

 R. Hamilton (9 a, p. 63) made however some experiments on the 

 croaking of the fresh-water drum-fish, which is provided with 



*Since this paper was written I find that Professor Albrecht of Brussels laid stress 

 on the ventral connection of lung-; and the dorsal position of the swim-bladder and its 

 duct, and strongly opposed the homology of the swim-bladder and lungs. 



