104 THE ELEMENTARY NERVOUS SYSTEM 



reaches the much more centrally located sphincter. In 

 the region of the sphincter of Aurelia, Rhizostoma, and 

 other such jellyfishes, these nervous bands spread out 

 diffusely over the whole muscle layer, producing thus a 

 nervous layer more superficial in position than the muscle 

 on which it rests. 



The earlier workers were not able to state with cer- 

 tainty the mutual relations of the elements in this nervous 

 layer. The prevailing opinion was that the layer was 

 composed of bipolar nerve cells. Eimer (1878) described 

 the processes from these cells as branched and stated that 

 the branches from various cells united to form a net- 

 work, a state of affairs that Schafer (1879) was unable to 

 confirm. Nor does the account of the nervous system of 

 Rhizostoma, as given by Hesse (1895), lead to the con- 

 clusion that a true network is present. With improved 

 histological technique Bethe (1903, 1909), however, 

 showed that the nerve plexus spreading over the sphinc- 

 ter of Rhizostoma is a true nerve-net in which the proc- 

 esses from the various nerve cells are continuous. This 

 nerve-net overspreads the surface of the sphincter as a 

 network, in which the processes from the cell-bodies, 

 though limited chiefly to a plane parallel with that of the 

 sheet of muscle, are not all thus restricted, but in many 

 cases may be traced, on the one hand, distally in among 

 the surface epithelial cells and, on the other hand, prox- 

 imally among the muscle cells. In respect to their direc- 

 tions the nerve processes are very unlike the underlying 

 muscle fibers for while the nerve processes extend in a 

 great variety of directions, the muscle fibers follow a most 

 rigid arrangement and take a course circular in outline 

 and concentric with that of the jellyfish as a whole. Thus 

 on the outer surface of a very regularly arranged system 



