110 THE ELEMENTARY NERVOUS SYSTEM 



sphincter muscle and the nerve-net are not coextensive. 

 In Aurelia the sphincter forms a continuous circular band. 

 In RTiizostoma, on the other hand, it is composed of a suc- 

 cession of sixteen muscle fields, a pair between each pair of 

 the eight marginal bodies (Fig. 33). These muscle fields 

 are partly separated from each other by areas of interven- 



FIG. 33. Diagram of a portion of the bell of Rhieostoma seen from the oral side; m, 

 muscle field; n, area covered by the nerve-net but devoid of muscle. (Modified from Bet he. 

 1909.) 



ing non-muscular tissue over which, however, the nerve- 

 net extends. Consequently, it is possible to cut prepara- 

 tions from Rliizostoma in which one muscle field with an 

 attached marginal body is connected with its neighbor only 

 by an area of nerve-net (Fig. 34). When such a prepara- 

 tion is stimulated through its marginal body, not only 

 does the immediately adjacent muscular field contract 

 but also the more distant one. It is, therefore, clear that 

 in this case transmission from one muscle field to the next 

 is accomplished by the nerve-net and not by the muscle 

 fibers. 



Another piece of evidence bearing on this question has 

 been advanced by Mayer (1906, 1908). Cassiopea is a 

 jellyfish that possesses considerable powers of regenera- 



