JELLYFISHES 107 



waves, one to the right and the other to the left, around 

 the bell till they fuse and become obliterated in a region 

 opposite that from which they started. If such a bell is 

 cut into a long spiral strip with the one remaining mar- 

 ginal body at one end and the center of the bell at the 

 other, a wave of contraction can be started from the mar- 

 ginal body and will progress ordinarily over the whole 



FIG. 31. Diagram of the jellyfish Aurelia from which the central mass and seven of the 

 eight marginal bodies have been removed. The outline of the bell has been further compli- 

 cated by a system of interdigitated cuts. (After Romanes, 1893.) 



length of the spiral. A much more complex preparation 

 may be made by cutting out the center of a jellyfish bell, 

 and then complicating it by a series of incomplete radial 

 -incisions in alternation, one set starting from the inner 

 edge of the bell and the other from the outer edge (Fig. 

 31). A bell thus complicated by so intricate a series of 

 interdigitations will nevertheless transmit a wave of con- 

 traction completely around its tortuous length. In fact, 

 secondary interdigitations may be cut on the lines of any 



