136 ZOOLOGICAL PHILOSOPHY 



Observations. 



We have seen that the infusorians are infinitely small and fragile 

 animalcules without coherence, without a shape pecuUar to their 

 class, without any organs and hence without a distinct mouth and 

 alimentary canal. 



In the polyps the simphcity and imperfection of organisation, 

 although very conspicuous, are less than in the infusorians. Organisa- 

 tion has clearly made some progress ; for nature has already obtained 

 a permanent and regular shape for the animals for this class ; they 

 are all provided with a special organ for digestion, and consequently 

 with a mouth which leads into the ahmentary sac. 



Imagine a small, elongated gelatinous, highly irritable body, which 

 has at its superior extremity a mouth furnished either with rotatory 

 organs or with radiating tentacles serving as the entrance to an ahmen- 

 tary canal which has no other opening : and we shall have a good 

 idea of a polyp. 



Add to this that many of these httle bodies become adherent and 

 Hve together in a common hfe, and we shall then know the most genera] 

 and curious fact that concerns them. 



The polyps are more imperfect in organisation than the animals 

 of the following classes, since they have no nerves for feehng, no special 

 organs for respiration and no vessels for the circulation of their 

 fluids. 



TABLE OF POLYPS. 



Order 1. — Rotifeb Polyps. 



They have ciliated and rotatory organs at their mouths. 



Urceolaria. 



Brachionus (?). 



Vorticella [Infusorian. H. E.]. 



Order 2. — Polyps which form Polyparibs. 



[Hydrozoa, Anthozoa, Polyzoa, Sponge, etc. H. E.] 



They have radiating tentacles around the mouth, and are fixed in a 

 polypary which does not float upon the waters. 



(1) Polypary membranous or horny, without distinct hark. 



Cristatella. CeUaria. 



Plumatella. Flustra. 



Tubularia. Cellepora. 



Sertularia. Botryllus [Asoidian. H. E.]. 

 (2) Polypary with a horny axis, covered with an encrustation. 



Acetabulum [Alga. H. E.]. Alcyon. 



CoralUna [Alga. H. E.]. Antipathes (black coral). 



— Gorgonia (sea-fan). 

 Sponge. 



