Sargent. — Optic Retiex Api)aratus 



PLATE 6. 



Fig. 40. Aniia calva, adult. Sagittal section, anterior at right, through the ante- 

 rior portion of the niesenceplialic roof and posterior commissure, 

 showing tiie axons of the optic retiex cells uniting in the ventricle. 

 Combined from several adjacent sections. X 41. 



Fig. 41. Polypterus bichir, adult. Parasagittal section, anterior at right, through 

 the anterior mesencephalic roof and posterior commissure, showing the 

 relation of the optic reflex cells to the posterior commissure, and the 

 axons uniting in the ventricle to form Reissner's fibre. Combined from 

 several adjacent sections. X 41. 



Fig. 42. Polypterus bichir, adult. Parasngittal section, anterior at right, of the 

 anterior portion of the left optic lobe, some distance laterad of the pre- 

 ceding, sliowing some of tlie laterally lying optic reflex cells. X 87. 



Fig. 43. Ameiurus nebulosus, larva, 15 cm. Sagittal section of posterior end of 

 the spinal cord, showing Peissner's fibre and two posterior canal-cells. 

 X 900. 



Fig. 44. Lepidosteus osseus, larva, 1st day after hatching, 10 mm. Sagittal sec- 

 tion anterior at left, of mesencephalic and diencephalic roof, showing 

 the optic reflex cells whose fine axons project into the ventricle. The 

 posterior commissure is not yet developed. X 205. 



Fig. 45. Lepidosteus osseus, larva, 15 mm. Parasagittal section (tangential), ante- 

 rior at riglit, of posterior portion of spinal cord, in part tlirough the 

 central canal, showing the branches of Reissner's fibre entering the 

 cord. X 380 ca. 



Fig. 46. Lepidosteus osseus, larva, 25 mm. Sagittal section, anterior at left, of 

 the posterior end of spinal cord and ventriculus terminalis, showing 

 two posterior canal-cells. X 470. 



