OF POLYPES. 



39 



connection with it. They, as ah-eady mentioned, are found 

 Iodised in a sort of Fig. 5. 



cell (Fig. 5. a.) exca- 

 vated in a sarcoid crust, 

 which constitutes the 

 main bulk of the po- 

 Ivpiferous mass, and 

 which, in fact, is no- 

 thinof more than a mo- 

 dification of the bases 

 and outer skin of the 

 polvpes hardened by a 

 deposition of calcareous 

 granules and spicula, 

 and made more coria- 

 ceous in texture, to 

 bear with impunity^the 

 contact and ruffling of 

 the water.* This crust is accordingly a living irritable struc- 

 ture, permeated by tubes prolonged from the polypes and by 

 capillary canals, for the conveyance of water and nutriment to 



every part. 



The connection between the crust and the polypes is there- 

 fore of the most intimate kind, and if for conveniency the latter 

 are separately described, the reader should ever remember, that 

 this separation is a forced and artificial one. An asteroid po- 

 lype mass is known by the orifices of the cells forming on the sur- 

 face a mark more or less resembling a star, as commonly repre- 

 sented in maps— hence the name of the order: when the polype is 



* " Lorsqu'on observe les Alcyons dans leiir etat naturel, la ligne de demarca- 

 tion entre ces deux parties parait bien tranchie, et on pouvrait au premier abord, 

 croire ces petits animaux loges dans des cellules au pourtour de rouverture des- 

 qnelles ils adhereraient ; mais quand on eleve a I'aide d'un acide etendu d'eau, 

 le depit calcaiie dont la base du polype est environee, on voit qu'il y a entre 

 ces parties continuite organique, et que la ceUule polypifere n'est autre chose 

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

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

 mun n'est en effet autre chose que la rcsultat de I'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, j). VJH. 



