IV 



PHYLUM CCELENTERATA 



147 



Hermit-crabs is a case of commensoMsm : the hydroid feeds upon 

 minute fragments of the Hermit-crab's food, and is thus its com- 



Fu. 108. Hydra. A, vertical section of entire animal : B, portion of transverse section, 

 highly magnified ; C, two large ectoderm cells ; L>, endodenn cell of H. riridts ; E, large 

 nematocyst ; F, small nematocyst ; 6, sperm, a, ingested diatom ; bd. J, bd. 2, buds 

 chr. chromatophores ; cnbl. cnidoblast ; cnc. cnidpcil ; ect. ectoderm ; end. endoderm 

 ent. cm. enteric cavity ; ent. cav' . its prolongation into the tentacles ; fl. flagellum ; hyp 

 hypostome or manubrium ; int. c. interstitial cells ; in. pr. muscle-processes ; mth. mouth 

 mwl. mesogloea ; ntc. large, and ntc'. small nematocysts ; nu. nucleus ; of. ovum ; ovy. 

 ovary ; psa. pseudopods ; spy. spermary ; rue. vnruole. (From Parker's Elementary 

 Biology, after Lankester and Howes.) 



mensal or messmate ; and the Hermit-crab is protected from its 

 enemies by the presence of the inedible, stinging hydroid. 



L 2 



