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



and leads into a large subperitoneal space. These bands 

 spread in a radiate manner into the surrounding area, inoscu- 

 lating with each other earlj in their course, and bj-and-bj 

 forming meshes (PI. XI. fig. 4) all over the surface. The 

 ribs of the meshes are especially strong- in front, and most of 

 the large meshes also occur in this region. Moreover, here 

 and there certain thickenings of the elastic ribs occur, forming 

 small solid nodes. As shown in the sketch (fig. 4) the 

 larger meshes in front have their long axis antero-posterior, 

 and each has either a central longitudinal rib with lateral 

 bars, as in a leaf with its midrib, or numerous strong ribs 

 bind the sides of the long meshes transversely. There is indeed 

 great variety in regard to the arrangement of the central ribs 

 and veins, but the whole presents an elaborate and sometimes 

 a nearly regular series of reticulations. The latter closely 

 approach the great aperture of the sac posteriorly, as indicated 

 in the sketcli (fig. 3). The general aspect of the inner sur- 

 face of the air-bladder is thus less silvery than in many fishes, 

 apparently from the predominance of the lustreless whitish ribs, 

 and indeed is more evident on the outer surface of the ribs 

 after the superficial fibres are removed. The raised ribs 

 appear structurally to be modifications of the elastic tissue 

 usually found in such organs. 



The object of these varied reticulations and of the solid, 

 firm, and elastic ribs is apparently to increase the strength of 

 the huge air-sac without adding much to its bulk, while at 

 the same time very great elasticity is provided for. The 

 morphologist is likewise reminded by the leaf-like enclosed 

 areas of the further development of the principle as observed 

 in the lung-like organs of the Dipnoi. 



When removing the muscles of the dorsum a tumour 

 resembling a pheasant's ^^^ in size and shape was found. 

 It is solid and firm, presenting on section a border of 

 blackish pigment and a whitish centre. Microscopically it is 

 fibro-granular with many oil-globules, and the pigment is 

 either in masses or scattered thinly in stellate corpuscles. 



Note. — In my paper in the '■ Annals ' for June 1885, 

 p. 433, line ^ifar bubalis, Bloch^ read scorpius, L. 



EXPLANATION OF PLATE XL 



Fig. 1. Section across the long axis of a vascular rete. a, cavity of a 

 great vessel ; b, muscular (and elastic ?) wall of the same ; c, 

 mass of blood-corpuscles ; d, connective tissue, x 90 diam. 



Fig. 2. Heart of the tunny reduced to somewhat less than half-size, and 

 opened from the dorsal aspect, a, a, pouches in the hulbus 



