190 THE PHYSIOLOGY OF INSECT SENSES 



obtained in optomotor-type apparatus at high and at low intensities 

 with the curve obtained electrophysiologically. The behaviourally de- 

 termined curve obtained at low intensities showed a maximum at 

 480 ray.. The high-intensity curve shifted towards 540 my.. This shift 

 could, as Schneider pointed out, be due to the transparency of envelop- 

 ing pigments to long wavelengths, but were this true, the white-eyed 

 mutant should exhibit a maximum at 480 my., whereas it actually shows 

 a maximum between 510 and 540 my. (Antrum, 1955 a). The shift must 

 be due to the participation of a receptor of low threshold, the 'receptor 

 for twilight vision', whose maximum sensitivity lies at 480 my. and a 

 less-sensitive receptor whose maximum lies above 540 my. (Schneider, 

 1956). Walther and Dodt (1957, 1959) have not reported any shift. In 

 the back-swimmer (Notonecta) a shift in which red and yellow become 

 darker to the animal with advancing dark adaptation (as measured 

 by optomotor reactions) has been noted by Resch (1954) and Liidtke 

 (1953) and referred to as a Turkinje phenomenon'. 



POLARIZED LIGHT 



In 1948 von Frisch (1948, 1949) opened a new area of investigation in 

 insect vision by demonstrating that honeybees could distinguish 

 different quadrants of the sky in which the plane of polarization of 

 sunlight differed. This conclusion was based on the fact that: (1) bees 

 in the hive could orient their communication dances as long as they 

 were able to see a patch of blue sky, and (2) the orientation of the dance 

 could be altered by interposing a piece of polaroid between the bee and 

 the sky. Bees act as though the sun is at right angles to the plane of 

 polarization. Since then directional orientation in the presence of 

 linearly polarized light has been demonstrated in many arthropods 

 (for reviews see von Frisch and Lindauer, 1956; Waterman, 1960). 



Polarized Hght may differ in degree, in type (linear, elliptical, or 

 circular), or in orientation of major axis. Practically all polarized light 

 in nature is linear (Jander and Waterman, 1960), and only this type is 

 known to affect animals. Two basic explanations have been proposed 

 to explain its perception. The most direct and obvious explanation is 

 that the eye possesses a specific polarization analyser, that is, that 

 animals see the direction of vibration of polarized light as distinct from 

 such other characteristics as intensity and wavelength (von Frisch, 

 1949; von Frisch, Lindauer, and Daumer, 1960; Antrum and Stumpf, 

 1950; Vowles, 1950; Menzer and Stockhammer, 1951 ; Stockhammer, 

 1956, 1959; de Vries, 1956; Birukow and Busch, 1957; Jander, 1957; 



