PHOTORECEPTION 191 



Liidtke, 1957; Jacobs-Jessen, 1959; Waterman, 1960; Jander and 

 Waterman, 1960; and a number of investigators studying Crustacea). 

 An alternative hypothesis suggests that differential responses to 

 various planes of polarization of light depend only upon detection of 

 different intensity patterns (Baylor and Smith, 1953; Stephens, 

 Fingerman, and Brown, 1953; Bainbridge and Waterman, 1957, 

 Baylor and Smith, 1958; Kalmus, 1958, 1959; de Vries and Kuiper, 

 1958; Baylor, 1959a, 1959 b; Smith and Baylor, 1960). This later 

 hypothesis is consonant to two basic facts: (1) differential reflection, 

 refraction, and scattering of polarized light by environmental features 

 or dioptric elements of the eye (Waterman, 1954) can produce 

 quadrants of maximal and minimal intensities whose positions are 

 determined by the direction of vibration ; arthropods respond to light- 

 intensity patterns. In further support of the hypothesis is the lack of 

 convincing proof of the existence of a polarization analyser in the eye. 

 No direct positive proof has been presented to contradict the opposing 

 hypothesis. 



Support for the idea that the animals do see the plane of polariz- 

 ation as distinct from intensity patterns has recently been summarized 

 by Jander and Waterman (1960) in the following terms: 



(1) In Daphnia and the beetle Bidessus, which could be made either 

 positively or negatively phototactic, reversal of this sign caused a 

 reversal of response to ordinary horizontal light intensity patterns, but 

 had no effect on the response to the plane of polarization of a vertically 

 directed beam. Therefore, polarized Hght orientation cannot be due to 

 horizontal patterns due to scattering and reflection of polarized light. 



(2) In all animals, responses to horizontal patterns of Hght intensity 

 are of two sorts only, that is, towards or away, while four basic 

 orientation directions have been observed in a vertical beam of linearly 

 polarized light. Therefore, two different sensory mechanisms must be 

 involved. 



(3) Response to the direction of vibration of polarized light showed 

 smaller deviations from the maximally preferred horizontal intensity 

 patterns. Therefore, both reactions cannot be intensity responses. 



(4) When the dark intensity patterns due to the scattering of 

 polarized Hght are made artificially brighter, the crustacean Mysidium, 

 Daphnia, and Bidessus still respond as before to the plane of polariz- 

 ation. Therefore response to polarized light is not simply a photo- 

 tactic response to brightness. 



(5) The crustacean Mysidium can distinguish between horizontal 



