COLE. — IMAGE-FORMING POWERS OF VARIOUS TYPES OF EYES. 3(33 



tions from the anatomical conditions ; no test has been made to show 

 whether the physiological action supports the hypothesis. The eyes 

 of Bipalium are so small, and their axes so variously directed, that it 

 seems doubtful if the individual eyes can have more than a very gen- 

 eral directive function in the reception of light. Although in general 

 they open directly outward, — as mentioned by Jilnichen ('96), and as 

 may be seen in the photograph of a portion of the border of the head 



A 



I I 



^ 



C 



x> 



/. 



Figure 7. Various illuminations of the i>hmnriiin eye with light coming from 

 different directions. The optic cups are drawn too large in proportion to the 

 size of the liead. The arrows indicate the direction of the light ; the portions of 

 the interior of the cup not reached by the light are shaded. — From Hesse, '97. 



reproduced in Figure 8, — they are nevertheless not all accurately 

 oriented in that way ; furthermore, the position and direction of each 

 eye naturally varies with the movements and contractions of the ani- 

 mal. In general, however, they do open outward, as is represented 

 diagrammatically in Figure 9. It will be noticed that the eyes of any 

 particular region are so arranged that they usually receive light exclu- 

 sively from a direction normal to that part of the surface of the head 

 beneath which they lie, as indicated by the arrows. The efficiency of 



