DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 911 
dorsal folds (valvula cerebelli, fornix of GorrscHE, which seem to be present only towards 
the posterior border) are all much more evident in Anarrhichas. Behind this, the 
inner or inferior surface of the outer layer becomes richly folded, while the fusiform 
condition of the lower fold disappears, a nearly straight band taking its place. These 
folds continue until the optic ventricles disappear. In the salmon of the first day there 
are only a few smooth folds on the under surface of the roof of these lobes. 
In the region of the pituitary body in Anarrhichas, the trabecule are more elongated 
and more obliquely situated than in the salmon, where they are also more widely separated. 
The pituitary body is perhaps less flattened from above downward than in the salmon, 
but in both forms it has the same structure, viz., aggregated nucleated cells (Pl. XXIV. 
figs. 1 and 2). A band, apparently of connective-tissue, proceeds from the under surface 
of the brain to the pituitary body, and this band is in the main fibrous; while in the 
salmon it is composed of connective-tissue cells, the nuclei of which stain very deeply. 
A layer of connective-tissue separates it from the infundibulum. 
In each of these forms the pimeal gland—both as to position and _ histological 
structure—is the same, but the pale commissural fibres passing to the upper region of 
the mid-brain are proportionally larger in Anarrhichas, and therefore can be traced 
further into its substance (Pl. XXIV. fig. 1, pf). The central aperture of the thalamen- 
cephalon in front of the pineal gland is more capacious and better defined than in the 
young salmon, and it rapidly assumes large dimensions, and opens into the third ventricle 
inferiorly (Pl. XXIII. fig. 5, and Pl. XXIV. fig. 2). The ventricles of the optie lobes 
appear superiorly at the side, as in Anarrhichas, and the two rapidly merge into one 
chamber. The separation of the infundibulum from the peduncular region is more 
distinct, the connective-tissue being very apparent; but the arrangement of the parts is 
similar to that in the wolf-fish, though the infundibular cells are larger. 
The complexity of the brain, especially in regard to minute structure, augments as the 
larva increases with age. Thus, in the middle of March the radiate fibres of the mid- 
brain (optic thalami) to the optic lobes are largely developed, and the thicker cortical 
region is more clearly differentiated from the inner layers. Moreover, it is evident 
that the tori semicirculares posteriorly are now encroached upon by commissural fibres 
passing to the roof. 
A distinct and broad commissure appears in front of the pineal body, and is continued 
behind it, the posterior band being very evident, so that it may even be regarded as 
separate. Horizontal sections do not, however, sufficiently aid in deciding this point. 
Next, from before backward, is the commissure of the optic nerves inferiorly and in the 
neighbourhood of the infundibulum. Lastly, are other transverse bands which will be 
subsequently mentioned. 
Somewhat later a differentiation appears in the centre of the peduncular region, in 
the form of a rounded area with a cellular margin (Pl. XXIII. fig. 6); the vesicle in 
front and beneath the pineal gland becomes more or less obliterated; and the optic 
ventricles posteriorly show a diminished lumen on each side, for the fibres passing to the 
