()G(5 RADIATION BIOLOGY 



Purkinje shift in the spectral sensitivities at high and low intensities and 

 on comparisons with the sensitivity shown in Hering's famous evaluation 

 of a totally color-blind man. Recent work in comparable technics 

 includes that of Minnich (1940), in which reaction times measured for 

 white light and for four regions of the spectrum with "ecjual energy 

 content" were evaluated for 90 trials on 50 worms {Clitellio), with the 

 conclusion that, since the light-adapted and dark-adapted worms showed 

 maximum sensitivity in the same region of the spectrum, the photo- 

 receptors must contain only one photosensitive pigment and hence the 

 worms cannot distinguish different wave lengths. The opposite approach 

 is typified by that of Liche (1934) on Limnaea, in which these snails were 

 conditioned to a Y-shaped maze and distinguished between red and blue 

 over a wide range of relative intensities as long as the eyes were present; 

 brightness discrimination seemed to be a dermal function, but color vision, 

 an optic possibility. 



Color-vision studies have commonly provided contradictory results. 

 Thus several have reported definite color selection by spider crabs and 

 hermit crabs in the selection of "decorations" for the body, on the one 

 hand, and of dyed snail shells, on the other. Others found no evidence 

 to support these claims. Eyestalk compensatory reflexes have been used 

 toward moving fields of vertical colored stripes in Hippolyte and Carcinus. 

 Schlegtendal (1934) reported ability of the crab Leander to distinguish 

 between red and blue and red and green and of Crangon to distinguish 

 yellow from blue. Daphnia has been used widely for spectral-sensitivicy 

 investigations. Van Herwerden (1914) and Merker (1930) concluded 

 that Daphnia could see in the ultraviolet as well as in the spectral bands 

 visible to man; many of these workers credited the water flea with defi- 

 nite color vision. Related planktonic Crustacea were investigated with 

 reference to ultraviolet (finding responses following the Weber-Fechner 

 logarithmic relation) by Erhard (1913) with colored papers in the Hering- 

 von Hess tradition on Simocephalus. Scarcely any work has been done 

 on the spectral responses of myriapods or arachnoids other than the 

 studies on the xiphosuran Limulus by electrical methods and on Lithohius 

 by Scharmer (1935). 



Spectral responses of insects have been investigated primarily in rela- 

 tion to flower visits, to traplight collecting, or to destruction methods 

 for pests. The pollination problem has an extensive literature (see work 

 by H. Mueller, P. Knuth, von Kirchner, F. Knoll, and C. Robertson). 

 More technical studies include those of Milne and Milne (1945) and 

 Weiss (1943, 1944). In the caterpillar of the butterfly Danaus, Mayer 

 and Soule (1906) reported no kinetic reaction in the spectral regions 

 visible to man, but a strong positive response to ultraviolet. Jan da 

 (1931) noted pronounced negative response to ultraviolet (300-400 m;u) 

 in beetle larvae (Anthrenus), much less to visible light in human terms, 



