TIMOTHY H. GOLDSMITH 783 



of the spectruin. However, other methods must be employed to learn 

 the properties ol these receptors. By determining the relative energies 

 necessary to elicit ERG's of constant size, spectral sensitivity curves 

 have been made for both the ocellus and the compoimd eye of the 

 honeybee. These experiments also reveal the presence of receptor 

 systems maximally sensitive in different regions of the spectrum. 



The electrical responses of the compound eyes of worker bees to 

 light are complex in origin. The principal component is a maintained 

 negativity which seems to reflect depolarization of the retinula cells. 

 Neurons in the optic ganglion also contribute to the ERG, notably 

 a negative off-effect which is relatively more prominent at long wave- 

 lengths and in the light-adapted eye. However, the wave forms of 

 the responses of dark-adapted compound eyes to short (1/10 sec.) 

 flashes can usually be matched approximately at different wavelengths, 

 and these responses have been used as a basis for spectral sensitivity 

 measinements (20) . 



The dark-adapted compound eye of the worker honeybee is maxi- 

 mally sensitive in the green at about 535 m/x. Sensitivity extends into 

 the near ultraviolet, sometimes wath a second, smaller hump (20) . 

 The long wavelength maximum is shown in Fig. 4 (curve 1) . 



During adaptation with red or yellow light the spectral sensitivity 

 curve is changed. Sensitivity throughout the spectrum drops, but 

 relatively more at the long wavelength end. As the 535 m^ maximum 

 subsides, a peak appears in the near ultraviolet at about 340 to 345 

 iiifL (20) (Fig. 2) . The spectral sensitivity of the eye measured dur- 

 ing adaptation with a bright yellow-green light is shown in Fig. 4 

 (curve 2). Measurements do not extend to longer wavelengths be- 

 cause under such conditions of light adaptation the shapes of retinal 

 action potentials clearly differ at the two ends of the spectrum, and 

 it is impossible to obtain equal effects Avith widely separated wave- 

 lengths. 



The complementary experiment — measuring the spectral sensitivity 

 in the presence of an ultraviolet adapting light — does not show such 

 a striking change in the shape of the spectral sensitivity function. 

 There are two reasons for this. First, in the dark-adapted eye the 

 ultraviolet receptor system does not make so prominent a contribu- 

 tion to the ERG as does the green receptor system. Second, the sen- 

 sitivity of the 345 m^x receptor system decreases steadily in the blue 

 and green, whereas the 535 m/* receptor system maintains a significant 

 sensitivity through the near ultraviolet. For this reason a yellow 

 adapting light spares the ultraviolet receptor system, but an ultra- 



