PHOTORECEPTION 213 



facilitated by this motion. Even in those species (e.g., Cicindela) where 

 the ocellus consists of a larger number of retinal elements beneath 

 each lens, it is believed that all ocelli function together as a unit. 



Little is known about the parameters of the stimuli for stemmata. 

 It has been demonstrated that larvae are sensitive to a wide band of 

 the spectrum and seem to be able to respond to the plane of polariz- 

 ation (Wellington, Sullivan, and Green, 1957). Electrophysiological 

 studies have only just been undertaken with these receptors. The 

 ERG recorded with the active electrode on the ocellar nerve and the 

 reference electrode in the abdomen is simple in appearance. It con- 

 sists of a prominent positive wave followed at high intensities of 

 stimulation by a slow negative wave. It is believed to consist of two 

 components (Ishikawa and Hirao, 1960 a, 1960 b). The stemmata 

 become completely dark-adapted in about one hour and completely 

 light-adapted in about ten minutes. They follow flicker up to 

 25-30 per second. 



