ALCYONIUM. 507 



very intimately. In the interstices of these ramifications, which 

 are occupied by the gelatinous flesh of the animal, spicula of cal- 

 careous matter are deposited either in a circular or granular 

 form ; these, as in Sponges, give a general support to the whole 

 mass, though not consolidated in any one point. The general 

 vitality of the polypidom, however, would seem to be greater 

 than that of Sponge. If a single Polype be irritated, it with- 

 draws itself within its tube ; and the edges of the cell, which 

 were at first prominent, become nearly flat. IfVthe irritation be 

 more severe, several of the neighbouring Polypes also withdraw 

 themselves ; and if it be sufficiently prolonged, a collapse and 

 contraction of the whole polypidom is evident. The analogy is 

 very striking between this phenomenon, and that exhibited by 

 the Sensitive Plant, in which the effects of the irritation are 

 manifested at a greater or less distance, according to its intensity 

 (VEGET. PHYSIOL. 422). If, instead of the Polypes being 

 irritated, a portion of the general surface be touched, a curious 

 series of changes will take place. After some little time the 

 part touched becomes opaque, more dense, and depressed; and, 

 if the stroke be severe, this contraction will extend through the 

 whole mass, and the Polypes also will shrink. This is pecu- 

 liarly evident if the vessel containing the animal be smartly 

 struck ; since the shock will then be simultaneously felt through 

 the whole structure. Even the complete division of the poly- 

 pidom with a sharp knife, does not produce so evident an effect 

 as a slight shock, of which the effect is thus diffused. On the 

 other hand, when at rest and undisturbed, the Polypes protrude 

 their bodies, unfold their beautifully-formed tentacula, and take 

 in a large amount of water. This is transmitted through the 

 whole interior of the polypidom by its anastomosing canals, 

 and the mass becomes distended to twice or thrice its original 

 size; and from being firm and opaque, it becomes soft and 

 pellucid. 



1154. The general integument of this spongy mass has a firm 

 leathery texture, and sometimes contains a distinct calcareous 

 deposit; as does also that continuation of it, which forms the 



