JELLYFISHES 



111 



FIG. 34. Preparation of 

 two muscle fields from Rhizo- 

 stoma to one of which a mar- 

 ginal body is attached; the 

 preparation has been cut eo 

 that the second field is attach- 

 ed to the first, so far as its 

 neuromuscular relations are 

 concerned, only through the 

 nerve-net, n. 



tion. Wlien the superficial tissue on its subumbrellar 

 surface, epithelium, nerve-net, and muscle, is scraped off 

 over a given area, the regenerative recovery is of such a 

 kind that the epithelium and nerve-net appear soon and 

 the muscle layer somewhat later. It 

 is, therefore, possible to obtain in 

 Cassiopea regenerating individuals 

 in which the epithelium and nerve- 

 net have been re-formed over the 

 wound, but the muscles have not yet 

 appeared. Such individuals may be 

 cut into preparations in which two 

 masses of muscle are connected only 

 by a regenerated epithelium and 

 nerve-net. When one muscle field 

 in such a preparation is made to 

 contract the other field also quickly 

 contracts without the appearance of any movement 

 in the intervening region. Hence it must be admitted 

 that this intervening region, composed merely of epi- 

 thelium and nerve-net, has the capacity of transmitting 

 impulses to motion from, one of the muscle fields to the 

 other. This experiment, like that of Bethe, supports 

 the belief that transmission over the subumbrellar sur- 

 face of jellyfishes is accomplished by the nerve-net and 

 not by the muscle. 



The removal of all the marginal bodies from an acras- 

 pedote jellyfish is an effective way of rendering the bell 

 at least for the time being motionless. The same kind of 

 an operation can be carried out on a craspedote form by 

 cutting off the edge of the bell. In such cases the edge 

 usually carries with it some muscle tissue and will con- 

 tinue to pulsate for a long time, whereas the central por- 



