ZOOLOGY. 515 



3165. If the process of oxydation be augmented, then, 

 the tube's external wall indurates, becomes coriaceous, 

 and, lastly, ceratoid or horn-like in texture. The nerve- 

 tubes or the animal proper can now swim no longer, 

 since one kind only of motion is left it, namely, to pro- 

 trude itself out of, and then retract itself within, the 

 tube. It consequently falls to the ground, and while the 

 external mucus hardens, it clings to the former; such 

 are the Sessile or fixed Polyps. 



3166. Sessile Polyps having coriaceous or horny tubes 

 are called Plant-animals, Zoophyta, Phytozoa. 



3167. The adherent, dried and dead external tegu- 

 ment of the Polyp is called stem. Such a ramified stem 

 completely resembles a plant. 



3168. These woody or herbaceous stems are not rooted 

 in the earth, but have the power of adhering firmly to 

 every substance, to stone, glass, shells, and such like 

 bodies. They do not therefore draw in nourishment 

 through any root. 



3169. The ramification is often wholly plant-like in 

 character, resembling that of a shrub with separate ra- 

 mules, which even assume too the form of leaves, and the 

 animal tubes that of flowers. 



But frequently the ramules grow together also by their 

 extremities, giving rise to a trellis- work, the production of 

 which in plants is impossible. The soft animalcules, 

 which come in contact, cleave unto each other, and grow 

 together like wounded parts in the Sarcose animals. 



3170. Upon the surface of the ramules or the leaves 

 are apertures, out of which the mucous substance pro- 

 trudes the radiated mouth. But these mouths are fre- 

 quently, especially in the Cystic corallines, of two differ- 

 ent modes of formation. The one kind are cysts without 

 filaments, and contain ova, which are developed and fall 

 out. The others have filaments, which move and do 

 not produce ova. The former look like seed-capsules, 

 the latter like flowers with stamina, while the entire 

 stock resembles a monoecious plant. 



3171. With increased oxydation calcareous earth is 



