210 BULLETIN: MUSEUM OF COMPAKATIVE ZOOLOGY. 



diameter is 3 micra, in the bass 4 niicra. The mesocoele is occupied by 

 the large valvula, so that the torus extends only a short distance pos- 

 terior of the commissure. The axons from the torus-cells pass in many 

 small fascicles toward the ventricle by the shortest path through the 

 ' Schaltsttlck ' and emerge obliquely into the ventricle in front of the 

 posterior commissure in many small trunks which immediately unite to 

 form Reissner's fibre. Other small trunks (Fig. 68, fbr. hab. Reu.), 

 emerging from the anterior portion of the ' Schaltsttlck,' doubtless come 

 from the habenulae. 



Sparidae (151). In this family the conditions are very similar to 

 those in the preceding groups, but a few points of difl'erence may be 

 mentioned. In the scup, Stenotonius chrysops, the ependymal cells of 

 the ' Schaltsttlck ' are continued in long, coarse fibres, which run from 

 the ventricle obliquely toward the torus and tectum. This makes it 

 difficult to distinguish and follow the constituents of Keissner's libre. 

 It has, however, been determined that numerous fine trunks from the 

 torus-lobes converge toward the median plane and, passing obliquely 

 caudad and ventrad, fuse and emerge as the consolidated Reissner's 

 fibre at a point immediately below the posterior commissure. The 

 membrane lining the ventricle in this region is continued out over the 

 fibx'e as a thin, loose, men)branous sheath, which extends halfway 

 through the mesocoele. The relatively large fibre is 3 micra in 

 diameter. 



SciAENiDAE (155). In the squeteague, Cynoscion regalis, the optic 

 lobes are of great size, and extend far in advance of the posterior com- 

 missure, resulting in a much more capacious mesocoele than in the pre- 

 ceding forms. The torus- lobes hang suspended freely in the spacious 

 pocket of the mesocoele above the posterior commissure (Plate 9, Fig. 63, 

 tor. l(j.). At their anterior margin the lobes fuse with tlie posterior com- 

 missure. Caudad of the commissure and above the valvula, tlie lobes 

 rapidly diminish in size (see also Sargent, lOS*", Figs. 15-19). 



As the great mass of the torus lies above the posterior commissure, the 

 axons of its cells find their way to the ventricle almost exclusively 

 through the 'Schaltsttlck.' It is doubtful, in fact, if any remnant of 

 the pre-commissural tract remains. The axons of the torus-cells run 

 forward through the torus-lobes in small fascicles, which at the anterior 

 end of the torus are consolidated into trunks in which the separate axons 

 can no longer be distinguished. These bend around the posterior com- 

 missure converging in the median plane with those of the opposite side. 

 They traverse the ' Schaltstiick ' obliquely, ventrad and caudad, passing 



