212 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



ance, suggestive of its fibrillar nature (Fig. 54). Between this central 

 portion and the medullary sheath there is a clear hyaline ring. In 

 sections double stained with Congo red and Elirlich's hematoxylin, the 

 sheath takes the blue deeply, the central portion the red, the hyaline ring 

 remaining unstained. The medullary sheath is continued over the 

 divisions of the fibre to where they enter the ' Schaltstiick ' and divide. 



"Within the central canal numerous fine fibrils are given off from the 

 fibre to the walls of the canal. It is very difl&cult at times to distinguish 

 the fine filmy artifacts formed about the fibre from the actual processes. 



Labridae (160). An extensive collection of preparations of Tautogo- 

 labrus adspersus has been drawn upon for the study of the optic reflex 

 apparatus. Unfortunately, however, this is not a very favorable species 

 for this investigation, as the brain reaches a high degree of teleostean 

 complexity. The optic lobes are large and the tectum of great thickness. 

 The torus, though relatively not so large as in the preceding forms, is 

 yveW developed. The lobes of the torus remain quite distinct (Fig. /) 

 instead of fusing, as in the Salmonidae and other forms. Anteriorly, 

 where they are suspended in the mesocoele below the level of the tectum, 

 they have in section a rounded outline (Fig. /, tor. Ig.). Posteriorly 

 they taper away and lie more completely between the halves of the 

 tectum. Above the posterior commissure they are closely applied to 

 it and fuse with it (Plate 8, Fig. 57. See also Sargent, :03*', Figs. 6, 7). 



All portions of the apparatus are of small size, Reissner's fibre being 

 always less than 1 micron in diameter and consequently diflficult to find. 

 The difficulty of studying the anterior ending of this apparatus is com- 

 plicated by the presence of blood vessels in the ventricles of the optic 

 lobes. Large blood vessels run from the floor obliquely upward through 

 the lateral horns of the optic ventricle and branching enter the tectum. 



In young specimens 2 to 3 cm. long, Reissner's fibre may be 

 found through the entire length of the central canal to the extreme end. 

 The apparatus is probably fully developed at the time of hatching or 

 shortly after. Tlie cells of the torus are small, of uniform size, oval or 

 spherical in form, and have in general a bipolar appearance. They are 

 for the most part arranged in radiating bands or columns separated by 

 neuroglia fibres (Plate 8, Fig. 55, tor. Ig.). 



The axons of the cells find their way into the ventricle by one of two 

 patlis, — one entering the ventricle anterior to the posterior commissure, 

 the other entering dorsal and posterior to it (Fig. K). In the larval 

 tautog, 2 to 3 cm. long, the axons from the cells lying near the median 

 ventral surface of the torus enter the ventricle more or less directly 



