22 CNIDARIA. 



Phylum II. CNIDAEIA (JSTematophora). 



Eadial animals without pore-canals, and with thread-cells (or adhesive 

 cells) in their epithelium. Nerves and sense-organs. 



Class I. Hydrozoa (Polypomedusse). 



Polypes and medusae with digestive cavity sac-like, or narrowed 

 (gastro-vascular space). No gullet (stomodaeum). Development chiefly 

 by alternation of generations (medusoid sexual generation, or free- 

 swimming medusa3 as sexual animals). 



Order 1. Hydromedusce. Hydroid stocks devoid of mesenteric folds, 

 and with sexual medusoid buds or small craspedote medusae as sexual 

 animals. The nursing hydroid stock often possesses a horny cuticular 

 skeleton (perisarc) ; the sexual hydromedusse mostly small, with only 

 4, 6, or 8 radial vessels, muscular velum, naked marginal sense organs, 

 eye-spots (Ocellatae), or otocysts (Vesiculatae), double marginal nerve- 

 ring, and sexes usually separate. The blastula formed by delamination. 



Gymnoblastea-Anthomedusae, perisarc stops short at bases 

 of polypes ; medusas with ocelli, and with genital organs in the manu- 

 brium. Hydra viridis, H. fusca, solitary freshwater hermaphrodites, 

 devoid of perisarc or medusoid buds. Cordylophora lacustris, the 

 sexual buds remain attached. Eudendrium. Syncoryne sarsii, with 

 Sarsia tubulosa as medusa. Hydractinia and Tubularia, medusae 

 attached. Ccenograptus, Ordovician. Ctenaria ctenophora, a tran- 

 sitional form to the Ctenophora. 



Calyptoblastea-Leptomedusae, perisarc forms hydrothecae 

 and gonangia ; medusae with ocelli or otocysts, and genital organs in the 

 course of the radial canals. Sertularia and Plumularia with attached, 

 Campanularia and Obelia with free medusae. .!quorea, large medusa 

 with numerous radial vessels and marginal tentacles. 



Trachymedusae, craspedote medusae without gastral filaments, 

 and with a velum. Dense gelatinous umbrella. Sense-organs as ten- 

 taculocysts. The asexual hydroid generation has fallen out. ^Egina 

 and Geryonia with 6, Liriope with 4 radial canals. The freshwater 

 medusa, Limnocodium (? with a hydroid stage), possibly belongs here. 



Hydrocorallinae, polymorphic colonies with calcified cuticular 

 skeleton ; medusoid stage represented by sporosacs. Millepora. 

 Stylaster. 



Order 2. Siphonophora, free-swimming polymorphic stocks. Phy- 

 sophora hydrostatica. Physalia pelagica, Portuguese man-of-war. 

 Diphyes. Velella. 



Order 3. Acalephce (Scyphomedusse, Acraspeda). Medusae with gastral 



