INVERTEBRATE ZOOLOGY. 21 



Sub-order 1. Hydrida Simple, fresh-water polyps. Solitary in- 



dividnals reproducinj? asexually in sum- 

 mer and sexually at the approach of win- 

 ter. Do not form colonies. -^ Hydra. 



Sub-order 2. HydrocoraU ina e.. .Troi>icRl marine forms, polymorphic, in 



colonies, producing a sort of coral. 

 if MilUpora. 



Order 2. Hydro-medusae Sexual cells prodxiced by medusa, which 



may be 1) a free form produced by a ses- 

 sile or floating colony of polyps ; 2) a re- 

 duced form borne on a polyp colony ; 3) 

 a free-swimming form without polyp an- 

 cestors. All marine. 



Sub-order 1. Gymnobhistea-anthomedusae .. Ses.sile colonies of polj-ps, 



the separate individuals of which are 

 naked, and not protected by the perisarc. 

 The medusae possess ocelli and genital 

 organs in the manubrium, i^ Pennaria 

 with reduced medusae. 



t r, ■ ■, " from one colony. 



( ^«r.sirt=medusa ) 



Sa riiia= medusa 



Sub-order 2. Calyptoblastea-leptomedusae Sessile colonies of polyps, 



perisarc forming cui^s for the protection 

 of the individuals. Medusae 'with oto- 

 cysts and genital organs on radial canals. 

 -^ Campanularhi with free medusa. 

 if Sertidariii with reduced medusa. 



Sub-order 3. Trachyriiedump .. .Free-swimming medusa with direct de- 

 velopment (no polyps). Velum, 4-6 ra- 

 diating canals, and other characteristics 

 of hydro-medusae. Evidently forms 

 with suppressed polyp generation. [Prim- 

 itive forms that have not developed the 

 polyp form — Brooks.] 

 if Gei'yonia. Li Hope. 



