TIMOTHY H. GOLDSMITH 785 



of the population of receptors close to the tip of the electrode. Curve 

 3 in Fig. 4 is an average of the spectral sensitivities (at wavelengths 

 longer than 100 ny) of several drones in which the contribution of 

 the green-sensitive receptor system appeared to be small. The in- 

 teresting feature of this curve is that its maximum is at about 440 

 ni/ii. 



The final piece of evidence for a blue-violet receptor is biochemical. 

 The heads of bees contain a light-sensitive pigment formed of re- 

 tinenej bound to a soluble protein (18) . This pigment absorbs maxi- 

 mally at about 440 ny, and on exposure to light it bleaches, liberating 

 retinene. It is possible that it is not the only such photopigment 

 present in the bee; it accounts for no more than half the total retinene, 

 for in its isolation much of the retinene originally present in the 

 heads is lost. 



The absorption spectrum of the 440 m/x pigment is indicated by 

 the solid curve (curve 5) in Fig. 4. Note that one of the spectral 

 sensitivity functions (curve 3) is also maximal at 440 n\fx. The only 

 function known for retinene is the chromophore of visual pigments of 

 animals. This, and the observation that in bees the retinene is found 

 only in the heads, not the bodies, lend further support to the view 

 that the 440 n\jx photopigment of the honeybee is, in fact, a visual 

 pigment. If so, it is the only insect visual pigment that has been 

 described to date. 



The ocelli of worker honeybees also contain more than one kind 

 of receptor. The electrical response from the ocellus is diphasic; a 

 rapid positive deflection at "on" is followed by a slower negative 

 wave. In the near ultraviolet region of the spectrum the threshold 

 response consists entirely of the positive component; in the green 

 the threshold response is the slow negative wave. At higher intensities 

 responses evoked by widely separated wavelengths are similar and 

 include both components of the ERG (23) . 



Spectral sensitivity curves based on either component have two 

 maxima, one in the near ultraviolet, similar to the maximum described 

 for the compound eye, and one in the blue-green at about 490 m/x,. 

 The latter is shown by curve 4 in Fig. 4. The relative heights of these 

 two peaks vary, depending on w^hich component of the ERG the 

 spectral sensitivity function is based (23) . 



The dorsal ocelli are curious organs which do not resolve images. 

 Although in the worker honeybee they contain two kinds of receptors 

 functioning maximally in different regions of the spectrum, there is 

 no reason to believe that they play a critical role in the discrimination 



