526 



WM. A. KEPNER AND A. M. FOSHEE 



frontal section of a dark adapted eye shows a rhabdome that is 

 relatively low and greatly elongated; — the posterior end being 

 the thickest (figs. 5, 6, 7, 8 and 9). Transverse sections show 

 that these rhabdomes are concave (figs. 2, 3, and 4). Thus 

 we have the visual rod of this eye becoming low and elongating 

 in the dark and becoming high and rounding up in the Hght. 



Pigment cell and visual cell, therefore, of Prorhynchus in 

 the dark seem to make an effort to locate light by increasing 

 their receptive surfaces. 



Text-fig. 2 Outline drawing of dorsal ganglia and eyes of light adapted eyes. 

 Note the rounded contour of eyes and their forwardly directed axes. Taken from 

 living specimen. 



In addition to this reaction of the part of the elements of the 

 eyes, the eyes themselves change their axes with reference to 

 that of the body as a response to light and darkness. A living 

 specimen under strong illumination has the axis of its eye ante- 

 riorily directed at an angle of about 45 degi'ees from the axis 

 of the body ; while the eye of a dark adapted animal has its axis 

 laterally directed at- right angles to the axis of the body of the 

 animal (text-figs. 2 and 3). The dark adapted eye shifts its 

 position as if in this way also light were being sought. 



