CHAPTER VII 



NERVOUS TRANSMISSION IN SEA-ANEMONES 



A PLAN for nervous transmission in the body of a sea- 

 anemone was long ago described by 0. and R. Hertwig 

 (1879-1880). According to tins plan, it was believed that 

 the stimulation of any given group of sensory cells on the 

 surface of such an animal would excite activity in the sub- 

 jacent nervous layer, which, in turn, would call forth 

 contractions in the underlying muscles and thus originate 

 a response. This is well exemplified in the tentacles of 

 sea-anemones. When a strong stimulus is applied to the 

 ectoderm of these organs they immediately respond by 

 retracting due to a contraction of their longitudinal ecto- 

 dermic muscles. 



If, however, as is often the case, the sensory cells stim- 

 ulated are in the ectoderm of the animal and the respond- 

 ing muscles are in its entoderm, the course of transmis- 

 sion as advocated by the Hertwigs was believed to be 

 much less direct than in the former instance. In this case 

 the nervous impulses that arose in the ectoderm were be- 

 lieved to be transmitted from their region of origin 

 through the nervous layer of the ectoderm including the 

 oral disc to that of the oesophagus at whose inner edge 

 they passed over into the nervous layer of the entoderm 

 by which they were conducted to the appropriate ento- 

 dermic muscles. Thus the inner edge of the resophagua 

 was believed to be the region of nervous intercommunica- 

 tion between the ectoderm and the entoderm. Histo- 

 logical evidence that has led to the suspicion that this 



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