908 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



and, as Balfour and Parker observe, they are modifications of haemal processes, as 

 indeed had previously been noted, amongst others, by Muller and Gegenbaur. 



In the salmon, at the sixth or seventh week, cartilaginous ribs are present, and show a 

 well-formed head articulated to the parapophyses by a broad surface, apparently having 

 some elevations on its otherwise straight edge. The attached end is widened and shows 

 numerous cells ; but distally a single row of cells gives the tip a scalariform appearance. 

 In a few instances, the cellular structure was disconnected in the centre of the rib, the 

 intervening band consisting solely of a cord of the transparent matrix. The same has 

 been noticed by Grassi in a Cyprinoid. 



Brain. — In Anarrhichas, as in most Teleosteans, the chief features in the brain are the 

 great size of the mesencephalon, and the depth of the entire brain-mass. Probably con- 

 nected with this is the much more marked flexure of the anterior end of the notochord (PL 

 XXIV. fig. 1) in the larval wolf-fish than in the salmon. The fore-brain is shorter in its 

 antero-posterior diameter, and presents a comparatively larger area (in transverse section) 

 than in the salmon. At the origin of the optic nerves the proportional area of the brain- 

 surface is larger, and the breadth of the roof (mid-brain) greater than in the salmon. 



The shape of the brain-mass shows, indeed, great variation in post-larval stages of 

 various species. In the cod, T % inch long, it is, like Anarrhichas, rounded and com- 

 pact as a whole — the optic lobes in cross-section forming a semicircular mass — almost 

 equally composed of an upper layer of white matter, and a lower layer of deeply-stained 

 vesicular matter, the line of separation between them passing parallel to the surface of the 

 lobes. Posteriorly the roof and floor of each optic lobe thins out very much. In the 

 post-larval stage of the gurnard, about T % inch in length, the form of the brain is very 

 different — the conformation of the cranium being much flatter than in the Gadoid — the 

 brain-mass, especially the optic lobes, are markedly depressed and of disproportionate 

 superficial extent, and much thickened in the lateral portion. The vesicular and white 

 unstained parts form two well-marked strata of about equal thickness, a condition just 

 noted in the optic lobes of the Gadoids. As might be anticipated from the form of the 

 adult head, the post-larval Callionymus, -^ inch long, shows a brain considerably de- 

 pressed, especially in the middle line; but in the herring, when of slightly less size (viz., 

 -£-% inch), the flattened condition is even more remarkable, the optic lobes spreading out 

 laterally, and having thus a large superficial area. Hardly less striking is the condition 

 of the optic lobes in a form, probably Ammodytes (^ inch long). They are more rounded, 

 but, on account of their disproportionately large size, present a superficial surface quite as 

 noteworthy as the preceding forms. The deeply-stained vesicular matter forms a much 

 thicker stratum than the unstained white layer, and the line of separation is somewhat 

 irregular, and does not pass parallel to the superficies of this region of the brain. These 

 two layers in the optic lobes of the goby, ^ 5 ¥ inch long, differ still more from the Gadoid 

 and other examples mentioned above, the vesicular stratum in transverse section pass- 

 ing upward to a median point, and forming a deeply angular mass of great thickness, 

 sharply marked off by the sloping line of separation on each side from the thin and 



