1894.] On the Production of Sounds by certain Fishes. 439 



VIII. " Note on the Production of Sounds by the Air-bladder of 

 certain Siluroid Fishes." By Professors T. W. BRIDGE and 

 A. C. HADDON. Communicated by Professor A. NEWTON, 

 F.R.S. Received April 17, 1894. 



Dr. William Sorensen, of Copenhagen, has drawn our attention to 

 the fact that, in our memoir on " The Air-bladder and Weberian 

 Ossicles in the Siluroid Fishes," published in the ' Philosophical 

 Transactions' last year (vol. 184, pp. 65 333), "we failed to do justice 

 to the results of certain investigations which are embodied in his 

 paper, entitled " Om Lydorganer hos Fiske : en physiologisk og 

 comparativ-anatomisk Undersogelse," and published at Copenhagen 

 in 1884. In this paper Dr. Sorensen treats of the various methods 

 of sound production in Fishes in general, and in the case of the 

 Siluroid Fishes, describes the production of sounds by means of 

 certain stridulating mechanisms (friction of the dorsal and pectoral 

 spines), the " elastic spring " apparatus, and the paired extrinsic 

 muscles of the air-bladder in the Pimelodince. We do not here wish 

 to criticise his morphological conclusions, but to point out that, con- 

 trary to the assumption on pp. 270 and 301 of our paper, Dr. Sorensen 

 did make some experiments on living Fish. After describing the 

 nature of the "elastic spring " and the disposition of its muscles in 

 the South American Siluroid, Doras maculatus, on p. 88 of his paper, 

 he says, concerning this Fish : 



" Observations on the Production of Sounds. When one opens the 

 abdomen of a recently caught fish and quickly extracts the intestines 

 with everything that is attached to them so that the swim-bladder is 

 exposed, one can very easily perceive that the swim-bladder is in a 

 convulsive vibratory motion at the same time that the sound is pro- 

 duced. It is a very deep murmuring note, which is so strong that it 

 can be distinctly heard at a distance of 100 ft. when the animal is 

 out of the water. Unlike the sounds produced by the movements of 

 the pectoral fin, the tones produced by the swim-bladder are not 

 grating, and therefore not disagreeable to the ear. As far as I am 

 able to judge, the swim-bladder commands only one note, but this 

 can be stronger or weaker according to the will of the fish. If one 

 moves the fingers backwards and forwards over the swim-bladder, 

 one will soon perceive that the vibrating motion, beginning at the 

 same time as the sound, is strongest in the front, especially at the 

 " muscle-springs," and also that the muscles passing to these contract 

 at the same time that the sound is produced. If the muscles are cut 

 through, the sound is no longer produced. If one makes a little hole 

 in the swim-bladder, the sound will not be very much weaker ; but if 



