September 22, 1905.] 



SCIENCE. 



377 



undulatus) as an example of fishes in which 

 ' the air-bladder, without possessing special 

 muscles of its own, may, nevertheless, be 

 partially invested by tendinous, or partly mus- 

 cular and partly tendinous, extensions from 

 the muscles of the body-wall.' 



In the latest and best general work on 

 ichthyology, Jordan's ' Guide to the Study of 

 Fishes' (1905), this subject is but incidentally 

 touched on, the principal reference being that 

 ' the grunting noise made by most of the 

 Sciasnidse in the water is at least connected 

 with the large and divided air-bladder.' 



The most satisfactory account of the drxim- 

 raing function is that of Sorensen in his paper 

 ' Om Lydorganer hos Fiske ' (Copenhagen, 

 1884), the essential parts of which in the 

 present connection are restated in the article 

 cited by Boulenger. Sorensen acknowledges, 

 however, that he had examined only a single 

 dead specimen of a single scisenid species 

 (Micropogon undulatus), arid it is not clear 

 from his description that he recognized in 

 the muscle in relation with the air-bladder a 

 distinct organ rather than simply an offshoot 

 of one of the abdominal muscles. It is also 

 doubtful whether Dufosse (Annales des Sci- 

 ences Naturelles, XIX.-XX., 1874), whom 

 Sorensen quotes with approval, correctly in- 

 terpreted the cause of this phenomenon in the 

 drums, as this extract from Sorensen's paper 

 will show (italics mine) : 



By means of dissections [of Scicena aquila} 

 Dufosse has proved that tones can be produced 

 by the activity of most of the muscles, which, 

 coated with aponeuroses, are in immediate con- 

 tact with the diverticula of the air-bladder, but 

 that the most frequent and most intense tones are 

 produced by the activity of those muscles, which, 

 completely naked, are placed around the long 

 branches of the largest diverticula. The tones 

 may be of different pitch, in perfect accordance 

 with their being formed in different places (and 

 binder the influence of different muscles). 



The drumming act has been more thor- 

 oughly studied in the squeteague than in any 

 other scifenid species ; and the facts regarding 

 it, as determined by Professor Tower, may 

 here be repeated substantially as stated by me 

 in 1902 (I. c), but in somewhat greater detail: 



1. There is in the squeteague a special 



drumming muscle, lying between ' the abdom- 

 inal muscles and the peritoneum and extend- 

 ing the entire length of the abdomen on either 

 side of the median line, the muscles of the 

 two sides being united dorsally by a strong 

 aponeurosis. The muscle is of a decided red 

 color, in sharp contrast to the pale muscles of 

 the abdominal parietes, and the fibers are very 

 short, running at right angles to the long axis 

 of the muscle. 



2. The muscle, with the aponeurosis, is in 

 close relation with the large air-bladder, and 

 by its rapid contractions produces a drumming 

 sound, with the aid of the tense air-bladder, 

 which acts as a resonator. Experimentally, 

 the removal of the air-bladder or the section 

 of the nerves supplying the muscle abolishes 

 the sound ; if a removed air-bladder is restored 

 to its place the drumming is resumed; and 

 the substitution for a removed air-bladder of 

 any hollow, thin-walled vessel of suitable size 

 permits the resumption of drumming when 

 the special muscle is stimulated. 



3. The muscle exists only in the males, and 

 only the males are able to make a drumming 

 sound. 



It is probable the drumming mechanism 

 and function as existing in the squeteagues 

 are typical of a majority of the genera of 

 Scisenidse; but there are some interesting 

 variations in the limited niunber of genera 

 which I have been able to examine in the field 

 and laboratory. Thus in the croaker {Micro- 

 pogon undulatus) the special drumming mus- 

 cle is present in both male and female, and 

 both sexes make the drumming sound; while 

 in the so-called king-fishes or whitings 

 {Meniich-rhus) the drumming muscle and air- 

 bladder are absent in both sexes and no drum- 

 ming sounds are made. The seven commonest 

 genera of drum-fishes found along the At- 

 lantic coast may be thus classified with refer- 

 ence to the drumming function: 



i. Drumming muscle present in both male and 

 female, and drumming sound made by both 



sexes Micropogon. 



ii. Drumming muscle present only in male, and 

 drumming sound produced only by the male. 

 Pogonias, Scicenops, Cynoscion, 

 Leiostomus, Bairdiella. 



