Sargent. — Optic Reflex Apparatus. 



PLATE 4. 



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

 through the roof of the midbrain, showing the primitive flexure in tlie 

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

 tion. X 120. 



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

 through the anterior portion of the optic tectum, posterior connnissure 

 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 fine divisions 

 of the fibre of Eeissner 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 the cord and ventriculus 

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

 from the wall of the 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, ()tli 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 /j. 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 uppermost, 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. X 000. 



Fig. 31. Amia calva, Gth day. Sagittal section of tlie posterior extremity of tlie 

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

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



