Prof. M'Intosh's Notes on the Tunny. 335 



The ventricle of the heart forms a great muscular triangle 

 nearly 6 inches in its longer boundary, such as at the base or 

 along the convex edge. This powerful muscular mass con- 

 tains a comparatively small chamber which has an apical and 

 two lateral diverticula besides the great channel into the 

 bulbus. Each of these has various pits in the muscular walls. 

 The external layers have their fibres mostly in the long axis 

 of the sides, so that they are thus differentiated from the more 

 transversely arranged inner region. The apertui'e into the 

 bulbus is defended by the two great valves, and its whole 

 inner surface is thrown into a somewhat symmetrically 

 arranged series of elastic pouches, which by their disposition 

 probably perform some of the functions of the Elasmobranch 

 conus^ since their posterior folds (PI. XL lig. 2, a, a) appa- 

 rently form pockets in action. A similar condition is present 

 in the swordhsh, as represented by Dr. Giinther*. 



The auricle is a large and comparatively thick muscular 

 chamber with a complex \\Qi\NOxk oi musculi pectinati ^cixXXQXQdi 

 over the surface. 



The large quantity of the circulatory fluid in this fish was 

 very marked, especially as it remained fluid. The appearance 

 of the muscles and other parts renders it probable that the 

 species would afford interesting results in regard to tempera- 

 ture-observations. This is the more likely since Dr. John 

 Davy found the temperature of the blood in the deep-seated 

 muscles a little below (?) the gills in the bonito {Thynnuft 

 pelamys^ Cuv. & Val.) to be 99° F., whereas the temperature of 

 the surface of the water was in the region 80°"5 f- 



The swim-bladder is 3 feet in length and upwards of a foot 

 in diameter at its widest part. It has been briefly alluded to by 

 A. W. Malm in his account of a specimen from the Skagerak J; 

 but its interesting structure merits further study. In the 

 abdominal cavity the organ is situated close above the intes- 

 tine and other viscera, since the enormous subvertebral mus- 

 cular masses occupy the dorsal region and considerably limit 

 the space for its distention. Externally it has a peritoneal 

 coat on its free surface. Internally the whole surface is 

 beautifully reticulated by a vast series of raised whitish bands 

 which inosculate with each other. The main series of these 

 springs from the circumference of a large aperture (PI. XI, 

 fig. 3, a) an inch and a quarter in transverse diameter and an 

 inch and a half in antero-posterior diameter, which seems to 

 occupy the mid-dorsal region. The aperture, which is men- 

 tioned by Malm, is surrounded by a few warty processes, 



* Introd. Study of Fishes, p. 152, fig. 68. 



t Edinb. New Phil. Joiu-n. vol. xix. p. 325. 



1 Goteborg's och Bohuslans Fauna, 1877, p. 415. 



23* 



