THE MECHANISM OF THE SHADOW REFLEX IN CIRRIPEDIA. I. ELECTRICAL ACTIVITY IN THE SUPRAESOPHAGEAL GANGLION AND OCELLAR NERVE

¹ Department of Biology, Reed College, Portland 2, Oregon, and the Marine Biological Laboratory, Woods Hole, Mass.

1. The electrical activity of various parts of the nervous system under changing conditions of illumination in four species of barnacles has been studied.

2. The primary event at the photoreceptor is an "on" response that takes the form of a simple ERG similar to that described for the retinula cells in a number of other arthropods.

3. Evidence is presented that suggests that this information is transmitted to the second order neurons in the supraesophageal ganglion via electrotonic spread, but this cannot as yet be regarded as conclusive.

4. The second order neurons respond in a pure "off" fashion and are inhibited at "on." In Balanus this response, monitored at the circumesophageal connectives is tonic, while in Lepas and Mitella, recordings at the same position display a phasic response. It is suggested that, at best, third order neurons are responsible for the phasic response in the latter two genera.

5. Evidence is presented that both the primary "on" response and the second order "off" response are graded with intensity of illumination.

6. Failure to respond to multiple shadows is evident in the motor output of all species except Mitella, in which the stalk nerves respond repeatedly to multiple shadows. A possible explanation for the latter and a possible advantage of the former is offered.

This article has been cited by other articles:

				S. Ozawa, S. Hagiwara, K. Nicolaysen, and A. E. Stuart Signal Transmission from Photoreceptors to Ganglion Cells in the Visual System of the Giant Barnacle Cold Spring Harb Symp Quant Biol, January 1, 1976; 40(0): 563 - 570. [Abstract] [PDF]