232 CCIXENTERATA 



compact masses. Aslrinii;ia domr (fig. ^oj"), only coral in New England; Aslnva; 

 brain corals (Ca-Ioria, lig. 204, Maiiiciiui); Fat'ici (fig. 205). (2) Eungiacea, 

 or mushroom corals, no theca. Some colonial, others (Fimgia) solitary. A 

 sort of strobilation in development. (3) PoROS.-v, with skeleton porous like a 

 line sponge. Miidrcpora* deer's-horn coral (tig. 206), Porilcs, Aslroidcs. 



Fig. 206. — Mddrcpora crylhra-a (after Ivlunzingcr). 



Class IV. Ctenophora. 



The Ctenophores e.xcel all animals, even the mctlusa\ in transparency 

 and delicacy of tissues; many are so soft that a strong current tears them, 

 and no attempts to preserve theni have been successful. The bodv is 

 biradially symmetrical; i.e., is di^-ided by lioth sagittal and traiis\erse 

 planes into symmetrical hahes. Sitice the kmgitudinal a.xis is usually 

 longer than the others, which are generally equal, the bodv is usually 

 oval or pear-shaped. In Cesium the sagittal axis is grealh' longer, gi\ing 

 the animal the form of a bantl, whence the name '\'enus girdle.' 



The bulk of the animal is composed of a soft jellv with connecti\e- 

 tissue cells, jienetrated in ever)- direction bv polvnucleale muscle cells 

 (lig. 50) branched at their ends and apparenlh- inner\a(ed by special 

 nerve cells. On (he outer surface is a layer of ectoderm, while in the in- 

 terior is a system of branched entodermal canals. 



At the bottom of a depression (fig. 207, s) at the aboral ]iole is a thick- 

 ened patch of ectoderm, the sense body, a (vjjical slalocvsl (Tig. 20S). 

 The thick sensory ejiilheliiim forms a shallow groo\e, strong hairs which 

 rise from the edge of the groo\e arch o\er it, enclosing a space to be com- 

 pared to an incom])lele vesicle. In (he centre is a spherical mass of stato- 

 liths, supported on four bundles of S-shapcd agglulinale cilia. From 

 these bundles of cillia eight bands of tJ-iickcned epithelium, at lirst in pairs 

 (lig. 200, 7i'.v), later diverging, pass to (he oral pole (lig. 207, r). These 

 ■mcridioiuil bauds (so called from (heir course) consisi in part of ciliated 

 epithelium, in part of the characteristic 'condis' which arc the locomotor 



