PHOTORECEPTION 187 



of a receptor maximally sensitive at about 440 m[i has been demons- 

 trated in the drone (Goldsmith, 1958 b). Furthermore, Goldsmith 

 (1958 a) has found a retinene-containing pigment with a maximum 

 absorption in the blue-violet (440 m|i.). 



Studies of the cockroach eye have also revealed the existence of 

 more than one type of receptor (Walther and Dodt, 1957, 1959; 

 Walther, 1958 a, 1958 b). In the dorsal area of the eye the sensitivity 

 maximum to ultra-violet is higher than that to blue-green; in the 

 ventral part of the eye it is lower. Whereas the ventral area shows a 

 single-peaked (507 m,u.) sensitivity curve that is unaltered by the state 

 of adaptation, the dorsal area shows indication of another peak in the 

 ultra-violet. Adaptation with monochromatic lights changes the rela- 

 tive spectral sensitivities, and colour specific differences occur in the 

 shape of the ERG. 



For Drosophila Hamilton (1922) had produced evidence for the 

 existence of a system sensitive to blue-violet and one sensitive to blue- 

 green by specific wavelength adaptation. Fingerman and Brown 

 (1953), employing a similar technique, concluded that Drosophila also 

 possesses sensitivity in the red (650-675 mpt). 



The blowfly Calliphora is unique among the insects studied in that 

 the spectral sensitivity curve of its eye, as measured electrophysio- 

 logically, exhibits three maxima: ultra-violet, blue-green, and red 

 (Autrum and Stumpf, 1953 ; Walther and Dodt, 1958 a, 1958 b). There 

 is a discrepancy of about 30 mjx between the positions of the green 

 maximum reported by the two papers. 



In their search for evidence of colour vision, Autrum and Stumpf 

 combined electrophysiological and flicker fusion techniques. After 

 adjusting the intensities of two monochromatic lights they flickered 

 them alternately. Thus during the period of stimulation there was 

 constant intensity of illumination but flickering wavelengths. If the 

 ERG showed with heterochromatic flicker ripple that could not be re- 

 moved by adjustment of intensities, then one could conclude that the 

 eye discriminated between the two wavelengths. The findings were as 

 follows: In the region 690-620 m\L discrimination is slight, but this 

 region is sharply distinguished from all other regions ; yellow to blue- 

 green (620-650 m[x) is distinguished from all other regions and dis- 

 crimination in this band is sharp (a restricted region between 570 and 

 590 m.[L cannot be distinguished from colourless light); blue-green 

 (480 m.\i) is distinguished from all other colours; on both sides of 

 480 m\i there is a region (450-500 m\i and 500-560 m^t) which is dis- 

 tinguished from all colours between 560 and 690 mfx. Autrum and 



