COELENTERATA 21 



chemical sense. Both Eimer and Romanes published physiological 

 papers in 1877-1878 on work done several years previously which 

 seemed to show that jellyfishes had the power of conducting im- 

 pulses in a complex manner along their subumbrellar surfaces. 



Taschenberg, 1877, was unable to find nervous structures and 

 considered that the muscles I'esponded directly to stimuli without 

 the aid of a nervous system. The Hertwig brothers, 1878, clearly 

 demonstrated the existence of a nervous system in medusae. 

 Schafer, '79, found a network of nerve fibers in the subumbrella 

 lying between the muscular layer and the ectoderm, but did not de- 

 termine anastomosis. Somewhat later Schlater, 1891, believed he 

 had found the true nervous system in the marginal sense organs, 

 but a clear recognition of nerve cells was again made by Kassianow 

 ten years later. He found a nerve plexus in Liicernaria and Cra- 

 tevoloplms. In the latter, tripolar ganglion cells are also found. 

 He shows sense cells and ganglion cells in direct association with 

 epithelial cells. 



Hesse, '95, in Rhizostoma shows the structure of marginal sense 

 organs in some detail and gives some indication of the nervous sys- 

 tem. Fibers run fi'om the eight marginal sense areas to a more or 

 less circular band which is somewhat poorly defined, and other 

 strands spread out over the subumbrellar muscular bands of the 

 jellyfish. The relation between cells was not clearly shown. 



Bethe, '09, was able to prove that the nerve plexus in Rhizo- 

 stoma is a true network. 



Romanes and others have shown that the bell of a jellyfish 

 could be cut in a most complex manner without preventing the pas- 

 sage of a stimulus for a contraction wave. 



If a single marginal body is stimulated, contraction waves 

 start both to the right and to the left of the stimulation until they 

 mingle and disappear. 



If the center of the jellyfish is cut out and the margin deeply 

 notched, the tortuous pathway of tissues thus formed is capable of 

 carrying a contraction wave. If a jellyfish with one marginal sense 

 organ is cut in a spiral strip, a wave of contraction may be started 

 at the margin which will run the whole length of the strip. 



A jellyfish cut so as to make two concentric rings with only 

 two slight connections between will carry the impulse from the outer 

 to the inner portion by this narrow bridge. If the jellyfish is cut 

 so as to form a long circular stretch, a wave may course for a long 

 period round and round the bell. Such a "trapped" wave has been 

 known to go for eleven days with no great decline in rate; or at the 

 rate at which it was traveling, it would have covered a distance of 

 four hundred and fifty-seven miles in eleven days, Parker, 1919. 



The removal of the marginal bodies of a medusa causes the 

 movements to cease for a time, but it may be made to contract by 

 electrical or chemical stimulus. Experiments by Bethe seem to show 



