Sakoent. — Optic Reflex Apparatus. 



PLATE 3. 



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

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

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

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

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

 Fig. 10.) X 50. 

 Squalus acanthias, embryo, 4 cm. long. Sagittal section of the brain. 



X 15. 

 Kaja erinacea, young, 16 cm. Parasagittal section of the middle portion 

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

 from three adjacent sections. X 160. 



Fig. 19. Kaja 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 ' Dachkern.' X 80. 



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

 of the mesencephalic roof, close to the cerebellum, showing the innne- 

 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 terniinalis. The posterior canal-cells 

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

 projected on the median plane. X 385. 



