156 



CCELENTERA. 



Examples : — 



Phtfuiilaria and Sertiilaria have sessile gonophores. 

 Campamda7'ia geniculata liberates the meclusoid Obelia geniciilata. 

 {b) HydrocoralliriDS. — Colonial forms which suggest the Hydractiniaa 

 in their polymorphism and division of labour, but are distinguished by 

 their power of taking up lime, and so forming "corals." The colonies 

 are complex and divergent, the medusoid persons are probably sessile 

 gonophores, but a simple male medusoid has been described. Millepora^ 

 Sty last er. 



[c] Trachymedusie. — These exist only in the medusoid form, and are 

 divided into two groups, Tracho- 

 medusce and Narcomedusce, accord- 

 ing to the position of the gonads. 

 Geryonia^ Car7narma^ Cuniiia^ 



Aeginopsis, 

 2. Order Siphonophorce. — Free 

 swimming colonies of modified 

 medusoid persons {medusomes}, 

 with much division of labour. 

 Physalia (Portugese Man-of-War), 

 Diphyes^ I'ek/Ia, Forpita. 



B. Class ScYPHOzoA. 



There are two types — polypoid 

 and medusoid — veiy rarely occur- 

 ring in one Ufe history. The gastric 

 cavity has partitions with gastric or 

 mesenteric filaments, and there is an 

 ectodermic gullet. The mesoglcea 

 generally contains migrant cells. 

 The reproductive cells are endo- 

 dermic. 



I, Sub-class ScyphomedusDe, or 

 Acraspeda — 

 Jelly fish with gastric fila- 

 ments, sub-genital pits, 

 and no velum — 

 (i.) Lucernarice. — Sessile 

 forms. Luteriiaria. 

 (2.) DiscomedusDs. — Active 

 forms, often with 

 complicated life his- 

 tory. Aio'elia^ Pe- 

 lagia, Cya^iea, Rhizo- 

 stoma. 

 (3.) ConomedusLie. — Forms with broad pseudu-veluni, and other 



peculiar features. Charybdea. 

 (4.) Peromedusce. — Forms with four tentaculocysts only. 

 Pericolpa. 



Fig. 49. — Diagram of a 



gymnoblastic HydromedusK. 

 (After Allman. ) 



gut ca-\'Uy ; 



ectoderm ; 



hydra like 



the same, 



«, Stem ; />, root ; c 

 d, endoderni (dark); 

 J\ horny perisarc ; g 

 " person " (hydranth); 

 contracted ; h, hypostome bearing 

 mouth ; ^, s.ic like reproductive bud 

 (sporosac) ; 111, a modified hydranth 

 (blaAtostyle) bearing sporosacs ; /, 

 medusoid "person." 



