PHOTORECEPTION 169 



a decay of the c wave. Up to 0-08 seconds the Bunsen-Roscoe law 

 held. The many differences in the profiles of the ERGs were interpreted 

 as being due to differences in the form and magnitude of the two 

 negative waves. 



Melanoplus was again studied ten years later (Jahn and Crescitelli, 

 1938; Crescitelli and Jahn, 1939) as were the grasshoppers Trim- 

 erotropis citrina and T. maritima (Jahn and Wulff, 1942). The ERG 

 was essentially similar to that reported by Hartline; however, this 

 time it was reported as beginning with a weak positive wave (a) promi- 

 nent in some eyes, absent in others, and abolished by light adaptation. 

 In addition, a negative off-effect {d wave) occurred in the form of a 

 small hump on the c wave. The moth Samia cecripoa was reported to 

 have a similar ERG except that a d wave was never seen (Jahn and 

 Crescitelli, 1939). But for Galleria mellonella Taylor and Nickerson 

 (1943) reported a, b, c, and occasionally (i waves. 



The ERG of the water beetle Hydrous triangularis showed in its 

 most complicated form (high intensity, night eye) a simple negative 

 profile consisting of b and c waves only, while Dytiscus fasciventris 

 in similar circumstances showed a, b, and c waves (Wulff and Jahn, 

 1943). On the other hand, Bernhard (1942) described the ERG of 

 Dytiscus as being a simple b and c wave. 



In the grasshopper Dissosteira Carolina the profile obtained was 

 totally negative, consisting oib and c waves and only occasionally a d 

 wave (Taylor and Crescitelli, 1944). The most marked departure from 

 form encountered was an occasional ERG, in which, after the initial 

 negative response to illumination, there was a long, slow, positive 

 swing. A similar ERG had been reported by Hartline (1928) for 

 Chortophaga viridisfasciata. The ERG of the cockroach Periplaneta 

 americana was reported as a simple negative wave (Ruck, 1958 a; 

 Walther, 1958 a, 1958 b), as were also the ERGs ofTachycines, Dixi- 

 ppus, and the nymph of AescJma (Autrum, 1948 a, 1948 b, 1950). 



For all of the species mentioned thus far everyone agrees that the 

 usual ERG is essentially a cornea-negative swing. Depending on con- 

 ditions and species, it may or may not have an initial a wave and a final 

 i/ wave. There may be negative and positive after-effects. 



Disagreement arises when the ERGs for Diptera and Hymenoptera 

 from different laboratories are compared. For Musca domestica 

 Hartline (1928) stated that the ERG was similar to that of the other 

 species he studied, i.e., a negative potential consisting of components 

 b and c, but in a later record (Hartline, Wagner, and MacNichol, 

 1952) the ERG appeared with a small positive a wave at the on-point 



