Saroent. — Optic Reflex Apparatus. 



PLATE 7. 



Figs. 47-52 are parasagittal sections, anterior at tlie left, of the anterior roof of 

 mesenceplialon, and torus longitudinalis, cutting the posterior cotn- 

 missure, and showing something of tlic mode of formation of Kciss- 

 ner's fihre in the ventricle. Some details of tiie branches of tiie tilne 

 have been drawn in from adjacent sections. 



Fig. 47. Ameiurus nebulosus, young, 4 cm. long. The midbrain roof is of the 

 primitive ganoid type. (Compare Figs. 25, 2(), Plate 4.) X 205. 



Fig. 48. Notropis cornutus, adult. Fascicles of Heissner's-fibre axons enter the 

 mesocoele from the posterior side of the posterior commissure. X H7. 



Fig. 49. Aliitera schoepfii, young, 15 cm. long, lleis.sncr's fibre is formed almost 

 exclusively from fascicles of axons entering the ventricle anterior to the 

 posterior commissure. X ca. 100. 



Fig. 50. Ifhombus triacanthus, young, 4 cm. long. Both the anterior and posterior 

 branches of Peissner's fibre are shown. X 120. 



Fig. 51. Salvelinus fontinalis. The section is soniewhat oblique; the anterior por- 

 tion of the figure is median ; the posterior portion parasagittal. Note 

 tlie anterior branches of Peissner's fibre entering the ventricle anterior 

 and ventral to the posterior commissure, and the posterior branches in 

 the recess above the commissure. X 120 



Fig. 52. Gadus caliarias, larvae, 15 mm. long. Peissner's fibre ventral to the pos- 

 terior commissure. X 385. 



Fig. 53. Cynoscion regalis, adult. Transverse section of posterior commissure 

 and Peissner's fibre. X 900. 



Fig. 54. Another section of the same, showing more clearly the medullary sheath, 

 and the punctate appearance in transviTse section of the axillary por- 

 tion, due to the cut ends of the constituent axons of Peissner's fibre. 

 X 1350. 



