POLYPS. 67 



and is now commonly used. MILNE EDWARDS makes a separate 

 class of these creatures, and places it amongst the Molluscs, after 

 the naked Acephala, or Tunicata. Their arms are beset with cilia, 

 which however are also remarked in some other Polyps, and conse- 

 quently are not a distinctive character of Bryozoa, as would seem 

 to be implied by the name Ciliobrachiata. To these Bryozoa belong 

 the genera Alcyonella, Eschar a, and Flustra. The remaining 

 Polyps we shall name, with EHRENBERG, Anthozoa. 



The simple stomach of the Anthozoa is, for the most part, sepa- 

 rated from the cavity of the body. In Actinia this space is divided 

 into many prismatic cells by partitions that stretch perpendicularly 

 from the outer surface of the stomach to the innermost surface of 

 the covering of the body. Similar partitions are found in many 

 Anthozoa^ though in much smaller number. One or more openings 

 conduct from the bottom of the stomach to the cavity of the body, 

 or to the general common cavity of the Polypstock 1 . In Hydra 

 there is no special cavity of the body, but the cavity of the stomach 

 is in immediate connexion with the walls of the body. It was 

 formerly erroneously believed that the stomach of this animal is 

 simply an excavation of its body, and that the structure of both 

 surfaces is the same. The internal surface is coated with conical 

 cells whose points are directed inwards 2 . The external surface, on 

 the contrary, is formed of flat cells, and contains oval vesicles, from 

 which a long delicate thread can be projected, (Angel-organ of the 

 Germans 2 ). TREMBLEY, amongst his many experiments on the 

 reproductive power of the fresh-water Polyp, even turned the body 

 inside out, like the reversed finger of a glove. Nevertheless, the 

 creature continued to live, and took food. This may be explained 

 by a change of structure, the consequence of the violence of the 

 experiment. In Bryozoa, the intestinal canal is freely suspended in 

 the cavity of the body: a longer or shorter oesophagus leads to a 

 muscular stomach, lined, in some cases, with horny teeth, closely 



GRANT, as early as 1827, had observed the reverting intestinal canal, and the vibrating 

 cilia on the arms of Flustra. Edinb. New Philos. Journ. ill. pp. 107 337. 



1 LISTEK, Philos. Transac. 1834, p. 371, PI. vm. fig. 3 in Seriularia. MILNE 

 EDWARDS in the new illustrated edition of CUVIER, Regne Anim. Zooph. PI. LXXX. in 

 Isis nobilis, &c. 



2 See CORDA, Nov. Act. Acad. Ccesar. Leop. Carol. Natur. Curiosor. Tom. xrm. 

 Ann. des Sc. natur. Tome vm. Zoologie, p. 363. 



52 



