068 RADIATION BIOLOGY 



without uncovering much information about visual mediation of the 

 stimuH provided. Among the Lepidoptera correspondence between lar- 

 val or pupal color and surroundings has been demonstrated and studied 

 experimentally, again with few new data on the visual functions that 

 may be involved. 



Summation of flickering light and migration of eye pigments under 

 illumination changes are two approaches to sensitivity which have yielded 

 helpful facts. Ability to recognize direction of movement in a circum- 

 rotating visual field was evaluated crudely in two crabs by Clark (1896) 

 and in the crayfish by Lyon (1899). Loeb and Ewald (1914) found good 

 correlation between action of the hydroid Eudendrium and prediction on 

 the basis of the Bunsen-Roscoe law^ for intermittent illumination. Hecht 

 (1921a) and Pieron (1925a, b) reported similar agreement in the clam Mya 

 as long as the summation occurred within 8-9 sec. Folger (1926) and 

 Hecht and Wolf (1932) extended the study further for Mtja. Muskens 

 (1904) reported a reflex in the pupils of the octopus as a reaction to a 

 rotating visual field but did not follow his observation with intensity or 

 spectral-distribution studies. Ewald (1913) used eye movements in 

 Daphnia as a criterion with a rotating sector wheel to adjust relative 

 intensities of two lights; hence he combined Talbot's law with the Bunsen- 

 Roscoe effect. Responses of the crustaceans Asellus and Cambarus have 

 been measured for flickering light without locating much new. Wolf 

 follow^ed these studies (1940) in terms of response to flicker when the 

 crayfish was stimulated monocularly or bilaterally, and found that the 

 more distant eye largely determined the threshold — that threshold is 

 dependent upon the number of visual elements per unit of visual field 

 undergoing transitions from an illuminated to a nonilluminated state 

 (see also Holloway, 1916). Wolf (1937) and Wolf and Zerrahn-Wolf 

 (1937) provided data also on the reactions of Limulus to flicker in terms 

 of compound-eye area stimulated. 



The more general work on flicker detection in insects includes a wide 

 variety of studies on the water strider Gerris, the back swimmer Notonecta, 

 dragonflies, butterflies, the flies Archytas, Eristalis, and PoUenia, the 

 diving beetle Dytiscus, and the honeybee. In the dragonfly and honey- 

 bee the maximum flicker frequency detectable was in the same range 

 (about 55 per second) as can be distinguished by the human eye, but 

 contrast between light and dark phases had to be ten or more times as 

 great to evoke a response in the insects. 



The relation between eye-pigment distribution and light intensity as 

 appreciated by the animal has been noted for some time. Rawitz (1891) 

 noted it in the retinas of cephalopods; Arey (1916) studied it in the retina 

 of the snail Planorhis. Szczawinska (1890) and Stefanowska (1890) 

 reported these effects in a wide variety of arthropods. Decapods and 



1 More properly the Talbot-Plateau law for flickered light. 



