CLASS POLYPS. 



155 



leads to the large stomach, which occupies the central part of the coriaceous 

 , >' '":'' " cylinder; between the mouth and the upper 



edge of the cylinder an immense number of 

 tentacules are ranged in a circular form, which 

 can either be outspread like the petals of a 

 flower, or retracted so as to be scarcely visible. 

 These are the organs of prehension, but they 

 have also much more important functions. 



VERETILLUM. Polypary stalk-like, perforated 

 longitudinally with four straight canals, which 

 open externally at its lower extremity, and have the polyp-cells terminating 

 in them, except at the lower fourth of their length, where the cells are de- 

 ficient ; polyps tubular, each with eight tentacules ranged about the mouth, 

 which leads to the stomach, and this opening into the polyp-cell. 



Lamarck describes two species of this genus, one Indian, V. Phattaides, 

 and the other found in the Mediterranean, V. Cynomorium, of which a very 

 interesting account has been given by Rapp, in the Nov. Act. Phys. Med. 

 Acad. Cos. Leap. Car. vol. xiv., who denies that either this genus or 

 Pennatula float voluntarily, but says that they have their lower end 

 plunged in the sand at the bottom of the sea, and that when placed in a 

 vessel of water they may be observed moving about on its floor, but never 

 swimming. He observes also, that, unlike the Freshwater Polyps, which 

 expand themselves, and seem to enjoy light, the Marine Polyps prefer the 

 shade, and that the polyps of the Veretillum, although expanding them- 

 selves in a darkened room, yet when brought into sunlight quickly fold 

 themselves up. Their stalk is freely pervaded by sea-water through the 

 four longitudinal canals which run through it, and communicating not only 

 with the stalk-like polypary itself, but also with the cells in which the 

 polyps are contained, and even with the tubular cavities of the polyps 

 themselves. This genus is phosphorescent, and its luminous character 

 depends on a thin mucus which overspreads its whole surface. 







Veretillum. 



HYDRA. The animals composing this genus are remarkable for their 

 power of reproduction. Trembley, of Geneva, to whose investigations, 

 published in 1774, we owe nearly all the 

 knowledge we possess of their structure and 

 habits, found that if a Hydra were cut into 

 several pieces, so many as forty, incredible 

 though it appears, each part soon became a 

 perfect Hydra. This animal is destitute of 

 any crvity around the stomach. The mouth 

 (a) is surrounded by slender tentacula, armed 

 with stinging bristles, with which it secures its 

 prey, and conveys it to its mouth. The 

 Hydra is common in stagnant pools, where it 

 may be found attached to aquatic plants, or 

 carried about on floating bodies. Its stomach, 

 which consists of a simple sac, is capable of 

 Hydra. being contracted or distended into various forms, 



a, mouth. It feeds on minute Crustacea or aquatic worms. 



CAMPANULARIA. Polypary plant-shaped, filiform, branched, homy ; 

 branches tubular ; cups campanulate,- 

 toothed at the margin, supported on 

 long tortuous peduncles. 



The Campanularus have consider- 

 able relation to the genus Sertvlaria 

 with which they were combined by 

 Linnaeus ; they are, however, readily 

 distinguished by the twigs not being 

 toothed at the sides by the little sessile 

 cups. In Campamdarice, the cups, 

 instead of being attached immediately 

 to the stem, are supported on foot- 

 stalks, which are of considerable length, 

 and tortuous at the base. 



CORALLINA. Polypary fixed, plant- 

 shaped, much branched, consisting of a 

 central stem, incmsted interruptedly 

 with a dense, calcareous, cortical sub- 

 stance ; cells inconspicuous ; polypi un- 

 known. 



There is still considerable obscurity 



Campanularia . 



with regard to the exact situation of the animals of this group of Corals in 

 the natural system, arising from the very 

 slight knowledge which is possessed of them. 

 They have, it is true, been seen by Lamouroux, 

 and by Ellis, but in so uncertain and unde- 

 fined a point of view, that the observations of 

 those Naturalists have thrown but little light 

 upon the relations which they bear to the 

 other groups. To the naked eye the cortical 

 substance of the Corallines in a dry state, 

 present not the slightest appearance of those 

 little cellules, which in other genera are known 

 to be the habitations of the animals ; it is, however, asserted, that when 

 recently taken from the sea, these pores may be observed over the whole 

 surface of the articulations. 



PLUMATELLA. Stem cylindrical, branching; simple, fixed by the base, 

 at the extremities of the stems and branches terminated each by a polypus ; 

 the polypi, with a depressed mouth, and ciliated tentacula, disposed in a 

 single row. 



Type of the genus, Tubularia repens, Mu'ller. Several species, inha- 

 bitants of the fresh waters of Europe ; two are found in Britain. 



Corallina. 



Plumatella. 



