IV 



PHYLUM CCELENTERATA 



167 



As in the lower Peromedusa?, the margin of the umbrella bears four ten- 

 tacles (t. ) and four tentaculocysts (f<: ), but the position of these organs is reversed, 

 the tentaculocysts being per- radial, the tentacles inter-radial. The tentaculo- 

 cysts are set in deep marginal notches, and the tentacles spring from conspicuous 



Fie. ll'.i. Pericolpa quadrigata. A, external view; B, vertical section; c!rc. s. circular 

 sinus ; en. cone; ft. f. gastric filaments; <ii>. y<>n:uls; UKJ. Iji. marginal lappets; m,il>. manu- 

 brium ; ml//, mouth; /'. t. pedal lobes; st. stomach; t. tentacles; tc. tentaculocysts; tn. 

 taenioles. (After Haeckel.) 



gelatinous lobes (/. ), which probably answer to the pedal lobes of the preceding 

 order. 



The margin of the umbrella is produced, in most cases but not in all, into a 

 horizontal shelf (rl. ), resembling the velum of the hydroid Medusa?, biit differing 

 from it in containing a series of branched vessels (end. lam'.} continuous with the 

 canal-system, and of course lined with endoderm. In the Hydrozoa, it will be 

 remembered, the velum is formed simply of a double layer of ectoderm with a 

 supporting layer of mesogkea. Owing to this fundamental difference, the velum- 

 like organ of the Cubomedusae is distinguished as the rdarium. 



