20 



ZOOPHYTES. 



3. 



tentacles (fig. 6). In the greater part of the species, minute calicles, 

 or little cups, but indistinctly visible to the naked eye, are arranged in 

 one or more series along the branchlets, and the cluster is a neat imita- 

 tion of the most delicate plumes (fig. 2), trailing vines, or mossy tufts ; 

 and, when alive, every calicle is the site of a polyp-flower. They 

 are occasionally but a few lines high ; yet others, no less minute in 

 their cells and polyps, attain a length of several feet. Quite a variety 

 of species may be gathered along our sea-shores, upon sea-weeds, 

 shells, or the rocks of the coast; and Hydras are common among the 

 duck-weed in almost any stagnant waters. 



12. The species are sometimes fleshy throughout, forming no cells 

 or corallum ; but, in general, the zoophytes have a very delicate cor- 

 neous or cartilaginous exterior, nearly or quite transparent, and the 

 same kind of horny membrane constitutes the calicle. In the Hy- 



droidea, having sessile calicles along 

 the branches, faint joint-like divisions 

 may be distinguished in the stem, yet 

 without a moveable articulation. The 

 corallum is commonly considered the 

 hardened cuticle. But other observers, 

 among whom is Dr. Fleming, make it 

 an inner tissue secretion ; and, if so, 

 it corresponds to the coral secretions of 

 other zoophytes. 



The calicle is usually an open cup, or 

 short tube, generally with a slight con- 

 striction or an imperfect cross partition 

 at base, partially separating it from 

 the stem below. They appear to the naked eye like mere points, 

 edging the branchlets (fig. 1); but, when enlarged, the cup-form is 

 brought out, as is shown in the annexed figures, 2, 3, 3, and 4. 

 Though sometimes toothed, the edge of the calicles is generally 

 entire, as in figures 9, 10, 11, on a following page. Each contains 

 the stomach and upper part of a polyp ; and, when unexpanded, the 

 circlet of tentacles is here withdrawn and concealed. The calicles 

 are arranged on one or more sides of the branch, and are either oppo- 

 site or alternate, though generally the latter. 



13. The tentacles are mostly slender tubular organs, arranged, in 

 a single series, around a small disk containing the mouth, and the 

 mouth, or the centre of the disk, is sometimes quite prominent, as is 



Sertukria. 



