58 ANTHOZOA. 



points of the body, we might, theoretically, deny the possibility of any 

 combination of actions ; and experiment teaches us that the assumption 

 is correct. 



(124.) If, when one of these animals is fully expanded, transparent, 

 and soft, any point of its surface be rudely touched, the whole body 

 does not immediately shrink, but only the point where the irritation 

 was applied appears to feel the impression ; this part shortly becomes 

 more dense, opake, and a depression is seen gradually to appear. If 

 the shock be severe, and extensively diffused over the body, the con- 

 traction slowly extends to the whole mass : the most violent local injury, 

 indeed, seems to be totally unperceived at remote parts of the body ; 

 whilst a general shock, such as striking the vessel which contains the ex- 

 panded polyp, produces a simultaneous contraction of the whole*. The 

 polyps, however, exhibit much greater irritability than, and their move- 

 ments, from their rapidity, form a striking contrast to the languid con- 

 tractions of the central portion : but that they have a community of life 

 appears improbable ; they seem to act quite independently of each 

 other: when one is touched, and suddenly retracts itself within its 

 cell, it is true that those in the vicinity will likewise not unfrequently 

 retire; but this circumstance may be accounted for by the sudden 

 movement of their neighbour ; for as the polyps are closely contiguous 

 to each other, there is no cause for urging a community of substance to 

 explain itf. 



(125.) It has been observed by Milne-Edwards J, in Alcyonidium 

 (fig. 25) a genus of Alcyonian zoophytes remarkable from the circum- 

 stance that its polypary, or common body, consists of two portions of 

 very different consistence, the upper part or trunk (c) being quite soft 

 and flexible, while the lower portion or foot (5), by which it is attached, 

 is of a hard and solid texture, that although under ordinary circum- 

 stances the movements of the individual polyps are quite independent of 

 the rest, a simultaneous contraction of the whole may be excited by 

 irritating the common trunk, and that to such an extent that, if the 

 stimulation be excessive, the whole of the soft portion of the polypary is 

 retracted into a coriaceous sheath afforded by the foot. 



(126.) On making a longitudinal section of one of the expanded 

 polyps (fig. 26, 1), the main features of its anatomy become at once re- 

 cognizable. The alimentary canal (c) is seen to be a cylindriform cavity 

 with membranous walls, occupying the axis of the upper portion of the 

 body, and extending from the mouth (b) to about the middle of the free 

 portion of the protruded polyp, where it terminates by a distinct orifice 



* Professor Grant, Lectures on Comparative Anatomy. Lancet for 1833-4, vol. ii. 

 p. 261. 



t Quoy et Graimard, Zoologie du Voyage de I'TIranie. Paris, 1834. 



$ Memoiresur un nouveau genre de la famille des Alcyoniens (genre Alcyonide). 

 Ann. des Sc. Nat. 1835. 



