PHYLUM CCELENTERATA 



167 



As in the lower Per.omeduso?, the margin of the umbrella bears four ten- 

 tacles (/. ) and four tentaculocysts (tc. ), 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 



imnb 



^ 



FIG. 110. Pericolpa quadrigata. A, external view; B, vertical section; clrc. s. circular 

 sums ; en. cone ; fj. f. gastric filaments ; yon. gonads ; my. Ip. marginal lappets ; r,inb. manu- 

 brium ; mth. mouth ; pd. 1. pedal lobes ; st. stomach ; t. tentacles ; tc. tentaculocysts ; tn. 

 tsenioles. (After Haeckel.) 



gelatinous lobes (L), 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 (vl. ), resembling the velum of the hydroid Medusae, but 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 mesogloea. Owing to this fundamental difference, the velum- 

 like organ of the Cubomedusse is distinguished as the velarium. 



