520 ALCYONIUM. 



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, and 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. 



1091. The general integument of this spongy mass has a 

 firm leathery texture, and sometimes contains a distinct calcare- 

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

 external coating of the Polypes themselves. From the integu- 

 ment the buds are produced, which originate in the spongy 

 structure itself, and are, in fact, prolongations of it. These are 

 traversed by canals, that branch off from those of the parent 

 mass ; and resemble pieces of Sponge in every important par- 

 ticular. It is not until the Polypes are developed at the ter- 

 minations of these canals, that the real character of the mass can 

 be positively stated. This is another example, in addition to 

 the number we have already seen, of the progressive development 

 of the higher forms of organised beings ; and of the correspon- 

 dence between its several phases, and the forms which remain 

 permanent in the lower parts of the scale. 



1092. The form and dimensions of the various species of 

 Alcyonia differ as much, as do those of the Sponges, to which they 

 bear so great an external resemblance. The Alcyonium digita- 

 tum creeps along the surface of loose stones and shells, forming a 

 thin fleshy crust, which rises up in irregular lobes or projections. 

 This small species is so abundant on some parts of our own 

 coasts, that scarcely a stone or shell can be dredged up from deep 

 water, whicli does not serve as a support to one or more specimens 

 of it. The particular form it presents, varies according to the 



