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 (PI. 
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, 4°; inch long, it is, like Anarrhichas, rounded and com- 
pact as a whole—the optie 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 3°; 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, 4 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, 3°; 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 
