20 LZ O}OFR LY ES: 
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 cel/s 
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 
Wr, without a moveable articulation. The 
ot 2 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 shght 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, 3a, 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circlet of tentacles is here withdrawn and concealed.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 
Sertularia. 
