238 Natural History of British Zoophytes. 



lypes and by capillary canals, for the conveyance of water and nu- 

 triment to every part. 



The connection between the crust and the polype is therefore of 

 the most intimate kind, and if for conveniency the latter are sepa- 

 rately described, the reader should ever remember, that this sepa- 

 ration is a forced and artificial one. An asteroid polype mass is 

 known by the orifices of the cells forming on the surface a mark 

 more or less resembling a star, as this is painted in maps — hence 

 the name of the order : when the polype is protruded from this cell 

 the body has a cylindrical figure, its upper disk surrounded by eight 

 short pectinated hollow tentacula, in the centre of which the mouth 

 is situated, leading into a distinct stomach, which is as it were sus- 

 pended in the centre, and sustained there by eight thin membranous 

 septa, which, stretched between the outer surface of the stomach 

 and the inner surface of the external tunic, divide the intervening 

 space into eight equal compartments. The base of the stomach is 

 perforated like the mouth, and from the. margin of the aperture de- 

 pend eight white tortuous filaments, which hang, either loose or con- 

 nected to a continuation of the membranous septa, in a wide abdo- 

 minal cavity, immediately underneath the stomach. This cavity is 

 again continuous with a tube which penetrates the common mass, 

 communicating freely by anastomoses with the tubes of other 

 polypes, and with a fine net-work of capillary vessels, formed in the 

 spaces between them, by means of small apertures in their walls. 

 (Fig. 4. *) In this manner there is effected a very free communi- 

 cation between the individuals of each common mass, so much so, 

 that the water swallowed by any one polype of it rapidly permeates 

 the whole, t By tracing the course of the fluid we may obtain 

 a clearer view of the organization. The water then enters the mouth, 

 and passes through the cylindrical gullet and stomach into the 

 abdominal cavity : thence part of it, flowing through the canals 

 formed by the septa stretched between the stomach and outer tu- 



le depot calcaire dont la base du polype est environnee, on voit qu'il y a entre 

 ces parties continuity organique, et que la cellule polypifere n'est autre chose 

 que la portion inferieure du corps du polype qui, en se contractant, rentre en 

 luimeme, comme nous l'avons deja vu pour les Alcyonides. Le polypier com- 

 mun n'est en effet autre chose que la resultat de l'aggregation intime de la por- 

 tion basilaire des polypes." Milne-Edwards in Ann. des Sc. Nat. iv. 336. an 

 1835. The student may compare this with Lamouroux's description of the Gor- 

 gonia. Corallina, p. 198. 



* A longitudinal section of Alcyonium digitatum. 



■f Milne-Edwards has proved this by a decisive experiment. — Ann. des Sc* 

 Nat. iv. 328 and 338, an 1835. 



