/. HTDROZOA: EJDROCOEALLIN^J. 



regenerate the whole animal. His experiments upon turning the animals 

 inside out have not been fully confirmed ; for in such cases the layers 

 resume their normal positions. Hydra grisea * (fusca). large brown 

 species ; H. viridis* green, from the presence of symbiotic algae. Pro- 

 tohydra ryderi* without tentacles. Polypodium hydriforme, parasitic 

 on sturgeon eggs in Russia, needs more study. The marine Haleremita 

 cumulans may belong here. 



Order II. Hydrocorallinae. 



Exclusively marine, forming colonies of thousands of individuals whose 

 calcareous skeletons so closely resemble true corals that they were asso- 

 ciated with them until the animals were studied. Millepora alcicornis* 

 stag-horn coral, in Florida. The rosy Stylasters occur in tropical seas. 



Order III. Tubulariae = Anthomedusae (Gymnoblastea). 

 As a rule these colonial forms with perisarc but without hydrotheca 

 produce anthozoan medusae, but there are forms like Clava * (pink, on 



FIG. 185. American Tubularian hydroids. A, Myrioihelia phryqiana (after Danielssen 

 andKoren); B. 6'arsi'a?-osari'a(afterFewkes); C, Monocaulispendula(a,fter Agassiz); 

 D, Clava leptostyla; E, Parypha crocea; F, Podocoryne mirabilis (after Agassiz). 



rockweed) and Hydractinia * (on shells inhabited by hermit crabs) 

 which have sporosacs. Indeed the genera Corymorpha * and Mono- 

 caulis * are only differentiated by the existence of medusae in the former 

 and of sporosacs in the latter. In the forms with alternation of genera- 

 tions different names are applied to the hydroid and medusan stages as 

 follows : 



HYDROID. MEDUSA. 



Pennaria. Globiceps. 



/Syncoryne. Sarsia. 



Bougainvillea. Hippocrene, Margelis. 



Gemmelaria. Gemmaria. 



Podocoryne. Dysmorphosa. 



