Sakoent. — Optic Reftex Apparatus. 



PLATE 3. 



Raja erinacea, adult. Parasagittal section of the midbrain roof. The 

 section is somewhat oblique, the anterior portion of the figure being 

 nearer tlie median plane than the posterior portion. X 40. 

 Raja erinacea, adult, same series. Sagittal section through the ependyniiil 

 groove, posterior commissure, and rigiit ganglion habenula. (Compare 

 Fig. 10.) X 50. 

 Squahis acanihias, embryo, 4 cm. long. Sagittal section of the brain. 



X 15. 

 Raja erinacea, young, IG cm. Parasagittal section of the middle i)<)rtion 

 of the roof of the mesencephalon, through the 'Dachkern.' Details 

 from three adjacent sections. X 160. 



Fig. 19. Raja erinacea, adult. Parasagittal section through the ' Dachkern.' 

 The cell at the left is shown in section, the two at the right show the 

 outer surface in perspective, with anastomosing arborizations of nerve- 

 endings. The pericellular neuroglia capsule is cut tangentially. 

 X 240. 



Fig. 20. Raja erinacea, adult. Sagittal section through the posterior portion of 

 the ' Dachkerti.' X 80. 



Fig. 21. Mustclus canis, adult. Parasagittal section through the posterior portion 

 of the mesenicephalic roof, close to the cerebellum, showing the imme- 

 diate proximity of the ' Dachkern ' cells to the ventricle. X 80. 



Fig. 22. Squalus acanthias, embryo, 4 cm. long. Sagittal section of the posterior 

 end of the cord and ventriculus terminalis. The posterior canal-cells 

 have been filled in from four adjacent sections, representing the cells 

 projected on the median plane. X 385. 



