172 THE PHYSIOLOGY OF INSECT SENSES 



(Wulff, 1950). Hartline (1928) considered that there were two negative 

 waves in the ERGs of insects (his A and B). Bernhard (1942) also 

 believed that in Dytiscus the ERG is made up of two negative waves, a 

 slow (S) and a rapid (R). In the dark-adapted state and at low in- 

 tensities R predominates; in the light-adapted state and high 

 intensities, S. He believed that R represents receptor activity and S is 

 in some way related to adaptation. Jahn and Wulff (1942) beHeved that 

 the ERGs of the grasshoppers Trimerotropis citrina and T. maritima 

 represent the sum of a positive and a negative wave. Taylor and 

 Crescitelli (1944) also assumed two components of opposite sign in 

 the ERG of Dissosteira, but did not completely abandon the idea that 

 the negative component itself might in fact consist of two waves. In 

 Galleria the a wave of the ERG was considered by Taylor and Nicker- 

 son (1943) to result from the interaction of two components. For the 

 more complicated, i.e., the *fast' type ERG, Antrum (1950) considered 

 that the negative off-effect is the homologue of the R component of the 

 'slow' type ERG and that the R component is a constant feature of all 

 ERGs. 



The compound nature of ERGs suggested that different components 

 have different origins. Roeder (1940) had found that extirpation of the 

 optic ganglion of Melanoplus did not abolish the slow wave of nega- 

 tivity characteristic of the ERG. For Dytiscus, neither removal of the 

 ganghon nor its cocainization altered the ERG other than to remove 

 the small spikes (nerve action potentials) that had been superimposed 

 on the slow wave (Bernhard, 1942). This smooth monophasic wave is 

 identical to that recorded when the electrodes are placed on the outer 

 and inner surfaces of the retina, and its size decreases as the leads are 

 removed proximally away from the retina. In some cases Bernhard 

 was able to record from a cornea from which the basement membrane 

 and all structures below it had been removed. In these cases the usual 

 large negative wave was obtained. This is clear evidence, at least for 

 Dytiscus, that the negative potential originates in the retinal cells and 

 not in the giant monopolar cells. Working with Trimerotropis, Jahn 

 and Wulff (1942) compared the ERGs of normal and deganglionated 

 eyes and concluded that the retina contributes a negative component 

 and the optic ganglion, a positive component. 



The origin of some of the components in *fast* eyes has been eluci- 

 dated by two very ingenious experiments of Antrum and Gallwitz 

 (1951). Successive portions of the optic ganglia of Calliphora were 

 removed and the ERGs recorded. As more and more of the ganglionic 

 mass (medulla interna and medulla externa) was extirpated, the 



