ANIMAL KINGDOM. 127 



2. Bryozoans Bryozoans, or moss-animals (so named with refer- 

 ence to the moss-like corals they often form), look like polyps, owing 

 to the series of slender ciliated organs surrounding the mouth, as repre- 

 sented in Figs. 152, 152 a, p. 119. 152 is magnified about eight times ; 

 and 152 a represents the animal, showing its stomach at s, and the 

 flexure in the alimentary canal, with its termination along side of the 

 mouth. The corals consist of minute cells either in branched, reticu- 

 lated, or incrusting forms. They are often cal- 

 careous; and such were common in the Silurian, 

 and still occur. Eschara, Flustra, Retepora 

 are names of some of the genera. 



Fig. 169 A represents a membranous species (called 

 Gemellaria loricata); a is the moss-like coral, natural 

 size; and b a portion of a branch, enlarged, showing the 

 cells. Bryozoans are also called Polyzoans. Bkyozoan, Gemellaria loricata 



IV. Kadi ate s. 



The sub-kingdom of Radiates contains three classes : — 



1. Echinoderms. — Having the exterior more or less calcareous, 

 and often furnished with spines ; and having distinct nervous and res- 

 piratory systems and intestine, as the Echinus (Fig. 143), Star-jish 

 (Fig. 144), Crinoid (Fig. 145). The name is from echinus, a hedge- 

 hog, in allusion to the spines. 



2. Acalephs. — Having the body usually nearly transparent or 

 translucent, looking jelly-like ; and internally a stomach-cavity, with 

 radiating branches. Ex., the Medusa, or jelly-fish (Fig. 140), which 

 generally floats free, when in the adult stage, with the mouth down- 

 ward ; the Hydra and allied species arc here included. 



3. Polyps. — Fleshy animals, like a flower in form, having above, 

 as seen in Figs. 137, 138, a disk, with a mouth at centre, and a margin 

 of tentacles ; internally, a radiated arrangement of fleshy plates ; and 

 living for the most part attached by the base to some support. Ex., 

 the Actinia, or Sea-Anemone, and the animals of ordinary corals. 



All these classes commence in the Lower Silurian ; and some of 

 their sub-divisions are therefore here mentioned. 



1. Echinoderms. 1. Holothurioids or Sea-slugs. — Having the ex- 

 terior soft, and throughout extensile or contractile, and the body 

 elongated ; mouth at one end surrounded by a wreath of branched 

 tentacles. It includes the Biche de mar, or Sea-cucumber. 



2. Echinoids or Sea-urchins. — Having a thin and firm hollow 

 shell, covered externally with spines (Fig. 143) ; form, spheroidal to 

 disk-shape ; the mouth below, at or near the centre, as the Echinus t 

 Fig. 143. 



