m l llllllLIIIMIIlliml(MftllirMlr|Wiln,,ni,,rrl.«lll|»ll | l|j[n|j | l j ;|j((|,||7|l/' l^ 



Retinal 

 cells 



Epidermis 



Pigment 

 cells 



Optic nerve 

 fibers 



Fig. 11.4. The eve of a planarian in vertical section; semidiagrammatic. The midHne of the 

 body is to the right in this figure; the retinal elements are stimulated only by light rays 

 entering the opening in the pigment cup. (Redrawn from L. von Graff, 1912, in H. G. Bronn, 

 hlassen und Ordnungen des Thierreichs.) 



Fig. 11.5. Major features of the 

 nervous system of a planarian, 

 Planana gonocephala. The small dark 

 flecks near the lateral margins repre- 

 sent sense organs; the small circles 

 mark the locations of dorsal and 

 ventral excretory pores. (From L. 

 von Graff, 1912, in H. G. Bronn, 

 hlassen und Ordnungen des Thierreichs.) 



Mouth 



Transverse 

 commissures 



319 



