22 INVERTEBRATE ZOOLOGY. 



Sub-order 4. Siphonophora Free-swimming colonies of polymorphic 



individuals representing both types (polyp 

 and medusa) and characterized by the 

 occurrence of a complex of several per- 

 sons, know^n as a Cormidium. In some 

 forms the medusae become free. -^ Vel- 

 lela ; in the majority the medusae are 

 rediiced, and develop germ cells (gener- 

 ally one egg in female) in the manubrium. 

 ■^ Physophora, Physalia. 



Class II. SCYPHOZOA Polyp form [ScyphulaJ with an invagi- 



nated protostoma. forming oesophagus 

 and secondary naouth, mesenteries pres- 

 ent, extending between oesophagus and 

 body-wall. Q-astrocoele containing mes- 

 enterial filaments. Medusa form {acras- 

 peda) large, without velum, with very 

 many branching radiating canals, with 

 square mouth and four genital poiiches, 

 with marginal lobes on sub-umbrellar 

 side. Body cavity containing gastral fil- 

 aments. Gelatinous middle laj'er cellu- 

 lar. 



Order 1. Anthozoa Polyps of Scyphula type, without medusa 



generation. Mostly coral producers. 



Sub-order 1. Hexacoralla Mesenteries and other parts in sixes. 



Many forms produce coral, showing the 

 arrangement of the mesenteries. 

 -^ Mefridhiin, Fungia. 



Siib-order 2. Octocoralla (Alcyonaria) Mesenteries and tentacles 



eight — coral consists of a horny axis 

 coated with a pol}'parium containing 

 sklerites. -^ Renilla. Cor'allium. 



Sub-order 3. Tetracoralla Parts in fours. All fossil. (Palaeozoic.) 



Order 2. Scyphomedusae Large medusae of the above descrix^ion 



(under Svypliozoa), which alternate with 

 reduced polyp generation of the Scyphula 

 type. ~jf Aurelia. 



