a very different appearance, being lightly tinted by fin^r, red- 

 dish brown pigment spots. 



Variability of Mare^inal Structures. 



One of the most striking peculiai^ities of this species is 

 its great variability. Undoubtedly sixteen is the normal num- 

 ber of the parameres, but we as often find specimens with seven- 

 teen or eighteen. The number of rhcpalia does not always 

 correspond to the number of parameres. There are often seven- 

 teen or eighteen of these and specimens have been found with as 

 many as twenty-three, Fig. 22. The introduction of additional 

 rhopalia seems to be a process analogous to the formation of 

 double monsters in higher animals. We find all stages from a 

 bifurcated rhopaliiun to two complete parameres in the place nor- 

 mally occupied by one. Indeed, we may trace the process further 

 back to forked tentacles in the scyphistoma larva. 



As in all Rhizostomae there are no marginal tentacles. 

 The margin of the disk is, when regular, divided into sixteen 

 scollops, the sinuses separating these being the sensory nich- 

 les. Each of these primary lobes is divided into five second- 

 ary ones, (fonning the 80 marginal lobes mentioned in the diag- 

 nosis) and from each of the shallow notches separating these 



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