S.vRGENT. — Optic Reflex Apparatus. 



PLATE 4. 



Fig. 23. Amia calva, just before hatcliing. Sagittal section, anterior at rijijht, 

 through tlie roof of tlie midbrain, sliowing the i)rimitive flexure in the 

 midbrain roof, and the optic reflex cells in an early stage of differentia- 

 tion. X 120. 



Fig. 24. Amia calva, 1st day after hatcliing. Sagittal section, anterior at right, 

 through tiie anterior portion of the optic tectum, posterior conunissure 

 and epiphysis. X 120. 



Fig. 25. Amia calva, 3d day. Sagittal section, anterior at left, through the 

 posterior commissure and anterior portion of the optic tectum. A 

 number of the optic reflex cells are shown, and axons of other similar 

 cells are seen entering the ventricle, and uniting. The tine divisions 

 of the fibre of Itcissner have been drawn in from two adjacent sec- 

 tions. X 200. 



Fig. 26. Amia calva, 6th day. Parasagittal section, anterior at left, of the same 

 region as the above. X 400. 



Fig. 27. Amia calva, 1st day. Transverse section of tlie cord and ventriculus 

 terminalis, showing, within the lumen and in process of dehiscence 

 from the wall of thi' cord, the cells which form the posterior canal-cells. 

 (The contents of the lumen have been filled in from two adjacent sec- 

 tions.) X 1200. 



Fig. 28. Amia calva, (ith day. Transverse section through the ventriculus termi- 

 nalis. A single posterior canal-cell nearly filling the lumen of ventri- 

 culus. X 1200. 



Fig. 29. Transverse section, same series, 30 ii anterior to the preceding. X 1200. 



Fig. 30. Amia calva, 2d day. Sagittal section through the posterior portion of 

 the cord. The anterior end is uj)i)ermost, ventral at the left. Two 

 posterior canal-cells, a, a, recently given off from the ventral wall of the 

 canal, and in process of differentiation, are shown, connected with a 

 third cell, y, by a protoplasmic strand. / 000. 



Fig. 31. Amia calva, 6th day. Sagittal section of the posterior extremity of the 

 cord and ventriculus terminalis. The posterior canal-cells and their 

 axons liave been drawn in from three adjacent sections. X 385. 



