Sargent. — Optic Reflex Apparatus. 



PLATE 2. 



Fig. 9. Mustelus canis, adult. A sagittal section of the midbrain roof, showing 

 the ' Dachkern,' and anteriorly a portion of Reissner's fibre within the 

 ependynial groove. The anterior portion of this section is strictly 

 median ; the posterior portion is somewhat lateral of the median 

 plane. X 15. 



Fig. 10. Mustelus canis, adult, same series. Parasagittal section (500 micra to the 

 right of the preceding figure) of the adjacent portions of the roof of 

 the diencephalon and mesencephalon. The section passes through the 

 posterior commissure and right ganglion habenula, and cuts the lower 

 lip of the ependymal groove, within which is Reissner's fibre. X 30. 



Fig. 11. Mustelus canis, adult, same series. Parasagittal section through the 

 trochlearis commissure and adjacent portions of the tectum opticum 

 and cerebellum. X 45. 



Fig. 12. Raja erinacea, at time of hatching, 12 cm. Transverse section through 

 the middle portion of the mesencephalon and the 'Dachkern.' X 25. 



Fig. 13. Squalus acanthias, ' pup,' at time of birth. Oblique parasagittal section 



through the diencephalic roof and anterior portion of mesencephalic 



roof. (The lower part of the figure is more nearly median than the 



upper portion, to show the course of the tractus tecto-fibrae Reissneris.) 



X40. 



Fig. 14. Mustelus canis, adult. Transverse section through the ependymal groove 

 and posterior commissure. X 30, 



