90G LIGHT AND LIFE 



maximum response at 340-370 m^, in the cases of Drosophila, house- 

 fly, honeybee, many beetles, the cockroach Periplaneta, etc. The 

 worker honeybee, according to Goldsmith's experiments, exhibits a 

 marked difference in spectral sensitivity when light-adapted and when 

 dark-adapted. Adapted to red light, the bee exhibits two nearly equal 

 peaks of sensitivity, at about 345 ny and 535 m^n. When dark-adapted, 

 responses of the ultraviolet receptor system are almost entirely masked 

 by the greatly enhanced sensitivity to green light. But one must dis- 

 tinguish sharply between the spectral sensitivity, as measured elec- 

 trophysiologically, and the behavioral response as manifested in photo- 

 taxis. It should be obvious that in color vision the behavioral response 

 may be preferentially evoked by some wavelength of light other than 

 that to which the eye is maximally sensitive. Ultraviolet seems most 

 potent in eliciting behavioral responses, but the eye may be more 

 sensitive to green or other wavelengths than to ultraviolet. Behavioral 

 preferences even change in the same insect with the phases of the life 

 cycle, or with a shift in the female from feeding behavior to egg-laying. 



The color vision of the honeybee has of course been the subject of 

 prolonged study by von Frisch and others. White light for the bee 

 must include some ultraviolet. "Bee-white" can be made from a 

 mixture of l57o ultraviolet (360 m^) -f 85 ^r white (xenon) or 

 85% 490 m^ blue-green (Daumer) . It is also possible to make "bee- 

 white" of mixtures of three monochromatic wavelengths: that is, a 

 mixture of 55^0 588 m^ + 30% 440 m,x can be substituted for the 

 490 m/i, blue-green in the mixture with 15% of 360 m^ ultraviolet. 

 Bee-purples also exist; and Daumer has concluded that bees have 

 three types of color receptors, for near ultraviolet, for blue-violet, 

 and for green-yellow-red. The measurements undertaken to determine 

 the relative energies required to obtain electroretinograms of constant 

 size reveal only two of these, namely, the receptor maximally sensitive 

 at 535 mix in the green, and the ultraviolet receptor at about 345 m^u,. 

 Evidence for the existence of a blue-violet receptor at present comes 

 only (a) from some measurements on the drone honeybee, which is 

 maximally sensitive at about 440 m/x; and (b) from biochemical 

 studies which indicate that bee heads (and not bee bodies) contain 

 a retincne, photosensitive pigment bound to a soluble protein, and 

 absorbing maximally at about 440 ny. This pigment bleaches like 

 rhodopsin, liberating retinene. The ocelli of the worker bee contain 

 two photoreceptors very like those in the compoinid eyes. 



Much work has also been done on the color vision of the blowfly 

 Cnlliphorn. Its spectral sensitivity has three peaks, at 350 m^, 500 m^, 



