^^37. 



THE POLYPI. 45 



tacles have only a single row of cilia, which move regularly and volunta- 

 rily, like the rotatory organs of the Rotatoria. 



By means of the currents produced by the cilia of their tentacles, many 

 Polyps draw towards their mouth light particles of food ; ''* others make 

 use of their ciliated arms to seize larger portions.'**' This a(;t is aided by 

 the nettling and various prehensile organs, which are more usually found 

 upon those Polyp-arms having no cilia. '^' These organs are found upon the 

 tentacles of Actinia, Edwardsia, Verctillum and Alcyonium, and without 

 doubt serve for the seizing of the prey as well as its retention until death. 



But these should not be confounded with special prehensile organs faumj 

 on the tentacles of certain species. These consist of a small coriaceous 

 capsule, from which the animal can project a kind of sting. '^"' By means of 

 these organs, the animal can attach itself like a bur to external objects^ 

 and not by suction, as is generally supposed. 



The circular or oval mouth is always situated in the centre of the an- 

 terior extremity of the body ; it is often surrounded by a lip formed of 

 circular fibres.''^' In a few species, the mouth projects like a cone at the 

 base of the tentacles. <^-' Vf\i\\i\\.e Phunatellae'^^''^'' the mouth is topped by a 

 tonguelet covered with rapidly moving cilia. Some of the Anthozoa-, 

 which capture animals of considerable size, can, in swallowing them, dilate 

 their mouth to an astonishing width. '^*' 



DIGESTIVE CAVITY OF ANTHOZOA. 



§37. 



The simple stomach of Anthozoa, which is of a variable length, opens 

 in general directly external by means of the mouth,'" and with a few 

 species, only, is there a muscular oesophagus.'-' 



With some, the stomach blends with the walls of the body,'^' but usually 

 it is more or less isolated. There remains, therefore, a cavity of the body 

 of variable size, and which is directly continuous with the cavities of the 

 arms. In those Polyps living in colonies, it is prolonged into canals trav- 

 ersing the corallum, and in this way the cavities of the bodies of all the 



7 Flustra, Eschara, Tubulipora and Crista- ment is still unprojected (see his Memoir in tho 

 tella. Nov. Act. physico-meilica XVIII. p. 300, Tab. XV. 



8 Actinina. fig. 5, 9, 10). Perhaps the oreans which Erdl 



9 Hydra,Coryne^Eleutheria,Se.rtularia,Cam- {Muller's Arch. 18-11, p. 424, Taf. XV. fig. 3) has 

 panularia and Alcyonium. seen upon the tactile lobules of yeretiUum cijno~ 



10 Such prehensile organs have been observed by morium a.Te of this kind. 



Quatrefa^es upon the clavate tentacles uf Eleu- U Actinia and Edwardsia. 



theria. He thinks also he has observed two mus- 'i- Hydra, Coryne. and Campanutaria. 



cles in their capsules, by which the retractile sting 13 Alcyonella and Cristatella. 



is projected (Ann. d. Sc. Nat. XVIII. 184'2, p. 276 U Actinia and Hydra. 



and 283, pi. VIII.; or Froriep''s neue Notizen, ^ Veretitlum, Alcyonium, Actinia ?i.rvi Hydra. 

 1843, No. 543, p. 230). The oval vesicles which 2 Edwardsia. See Quatrefa^es (Ann. d. Sc. Nat. 

 roughen the tentacles of Cam panularia, and which XVIII. pi. I. flg. 2 ; pi. II. fig. 1, 2). 

 Loven (/ri'e^/nann's Arch. 1837, 1, p. 252) has de- ^ Hydra. The stomach of the ann-polyps is not» 

 scribed as small Spinous warts, are probably of the as has been formerly supposed, a simple e.xcavation 

 same nature. In Hydra each hook-organ upon the in the body. It has proper walls distinct fi-om 

 arm is surrounded by a group of similar vesicles, in those of the body, by which, however, they are 

 the interior of which is a rigid bristle. These or- closely embraced. There is, therefore, in Hydrn 

 gans are here found only upon the arms. They no cavity of the body, and the cavities of the ten- 

 ure distinguished from the organs having hooks by tacles open directly into the stomach. This is also 

 their less size, and from their having no project- true of £/f:»/Aerja (Q«a«re/ag-e«, Ann. d. Sc. Nat. 

 ing filament. Corda has not properly distin- XVIII. p. 283). 

 quashed them from the hook-organs, wtiose fila- 



