PHYLUM CCELENTERATA 



147 



Bat the simplest members of the whole class, with the exception 

 of one or two imperfectly known forms which will be referred to 



Fig. 107t— Hydra, A, vertical section of entire animal ; B, portion of transverse section, highly 

 magnified ; C, two large ectoderm cells ; D, endoderm cell of H. viridis; E, large nematoeyst ; 

 F, small nematoeyst ; G, sperm, a, ingested diatom ; bd. 1, bd. 2, buds ; cJir. ehromatophorea ; 

 cnbt. cnidoblast; cnc. cnidocil ; ect. ectoderm; end. endoderm; ent. cav. enteric cavity; ent. 

 cav'. its prolongation into the tentacles ; Jl. flagellum ; hi/p. hypostome or manubrium ; int. c. 

 interstitial cells ; m. pr. muscle-processes ; mth. mouth : msgl. mesoglcea ; ntc. large, and ntc'. 

 small nematocysts ; nu. nucleus ; ov. ovum ; oi?y. ovary ; pad. paeudopods ; *py. spermary ; 

 vac, vacuole, (From Parker's Elementm-y Biology, after Laukester and Howes.) 



below, are the Fresh-water Polypes of the genus Hydra. The 

 entire organism (Figs. 27 and 107) consists of a simple cylindrical 



h 2 



