RETINAL PIGMENT OF PLANORBIS 



377 



both in the Hght and the dark, the pigment shows greater distal 

 migration at low (figs. 1 and 4) than at high temperatures (figs. 

 3 and 6), it follows that low temperature and light on the one 

 hand, and high temperature and darkness on the other, tend 

 to influence i)igment migration similarly. As the data show 

 (this being a logical corollary of the proposition just stated), 

 extreme distal migration is favored by the cooperation of light 

 and low temperature (fig. 1), whereas an extreme proximal 

 migration is best obtained at high temperatures in the dark 

 (fig. 6). It is pertinent to mention in this connection that the 

 pigmented processes at the higher temperatures in the dark 

 (figs. 5 and 6) were very thick as well as long. 



It will be noticed that in the light the values given in ])aren- 

 thesis (representing the results at room tem])erature co])ied 

 from table 1) are intermediate between the measurements at 

 the extreme temperatures; in the dark, on the contraiy, this 

 progressive relation does not hold. 



T.VBLE 4 

 Mcasiireiiicnls showing Ific nldliic distribulion of pigment in the excised eyes of 

 Planorbis at 2° and 30°C. in the light. The values are mean values expressed 

 in 7nicra and indicate both the thickness of the inain pigment mass {zonal meas- 

 urement), and the zonal measurement plus the length of the pigmented processes 

 {process measurement) 



2. EiJect on excised eyes. A few experiments were performed 

 to determine whether the temperature response is obtainable 

 in light-adapted eyes wliich are isolated from the body. In all 

 respects the method of experimentation was identical with 

 that employed when normal animals were used. 



Table 4 gi^-es the results from the small number of retinas 

 measured, an accident having destroyed the remainder of the 

 material. 



