DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 911 



dorsal folds (valvula cerebelli, fornix of Gottsche, 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 trabeculse 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 pineal 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 optic 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 



