CNIDARIA. 23 



filaments, lappets to umbrella, covered marginal sense-organs (tentaculo- 

 cysts), and central nervous system in the form of groups of ganglion-cells. 

 No velum. Development seldom direct (Pelagia, Charybdeidae ?), usually 

 with alternation of generations, the asexual generation being a short 

 broad scyphistoma, which strobilizes to produce medusae. The blastula 

 formed by invagination. 



Calycozoa (Lucernariee), fixed scyphistoma form without medusoid 

 stage. Lucernaria. 



Marsupialida, a high arched umbrella with 4-divided margin ; 

 four interradial tentacles, a pseud-velum, and four gastric pouches 

 wiih four lamellar genital glands on the partitions separating them. 

 Charybdaea. 



Discomedusae (Discophora), discoid acraspedote medusae with 

 8-divided umbrella-edge, slightly curved umbrella, genital glands in 

 floor of stomach, and at least eight tentaculocysts situated in notches. 

 Oral tentacles usually large. Pelagia noctiluca. Amelia aurita, 

 small, with branched radial vessels united by a ring-canal. Rhizostoma 

 Cuvieri, without marginal filaments, but with dorsal and ventral oral 

 frills ; the central mouth-opening of the Ephyra (young form) converted 

 later by coalescing folds into numerous suctorial pores. 



