500 SLONAKER. 



EXPLANATION OF PLATE XXX. 



Figs. 56, 57. Horned Toad (Phrynosoma cornutum). Fig. 56, vertical sec- 

 tion and Fig. 57, horizontal section through the center of each fovea. Fig. 56 

 shows also the width of the band-like area. Sections iS^u thick. X 32.3. 



Fig. 58. Pipefish (Siphostoma fuscum). Horizontal section through center 

 of fovea (i) of left eye. 2 indicates the position of nerve entrance. Section i8/i 

 thick. X 32.3. 



Fig. 59. Pipefish (Siphostoma fuscum). Section in a lower plane, showing 

 entrance of nerve (2) and the area (i). Section i8/i thick. X 32.3. 



Fig. 60. Chipmunk (Tamias striatus). Vertical section across area (a). 

 Section 24(u thick. X 32.3. 



Fig. 61. Turtle (Chelydra serpentina). Horizontal section through band-like 

 area. Section iS/x thick. X 32.3. 



Fig. 62. Frog (Rana catesbiana). Vertical section across band-like area (a). 

 Section 24/i thick. X 32.3. 



Fig. 63. Flounder (Paralichthys dentatus). Vertical section, showing com- 

 parative thickness of different layers of the retina. Section 30^ thick. X 32.3. 



