Variations Among ScyphomeduscB. 



573 



they be searched for critically they are seldom seen, since the hoods 

 and lappets serve to screen them from ordinary observation. 



It may be of some interest in this connection to refer to the 

 occasional appearance of twin rhopalia in regeneration, an extended 

 account of which I have elsewhere described.^ It has been found 

 that occasionally double rhopalia are produced in regeneration 

 where originally there was only a single one which had been excised 

 in the experiment. Rarely also during such experiments a super- 



16 



Fig. 1 6. Drawing showing three perradial canals and rhopaha in a given octomere, p. 

 Fig. 17. Sketch showing two octomeres a, a, with extremely simple canal systems. The positions 

 of the rhopalia are adradial. 



numerary rhopalium may develop at unusual points, as has been 

 described in the paper just cited. It is not at all improbable, 

 therefore, that in cases of injury the marginal portion of the 

 umbrella involved may be more or less modified during the process 

 of regeneration, and that marginal organs may appear in some- 

 what unusual places. It is not improbable that the somewhat 

 anomalous appearance shown in Plate I, Fig. 4, may be due 



'Regeneration in Rhizostoma pulmo. Jour. Exp. Zool., vol. i, p. 85. 



