ON POLYPS. 



ing the whole as a single animal, each part being in communication 

 with the rest, and thus participating in the feelings and movements 

 of the others ; whilst some consider each polyp as a distinct crea- 

 ture, independent of the rest. The solution of this problem is 

 a matter of some difficulty ; but there are several facts recorded by 

 observers, which may in some measure enlighten us upon the sub- 

 ject. From the absolute want of nervous filaments, which 

 might bring into communication distant points of the body, 

 we might theoretically deny the possibility of any combina- 

 tion of actions ; and experiment teaches us that the assumption 

 is correct. 



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 the point only where the irrita- 

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

 becomes more dense, opaque, and a depression is seen gradually to 

 appear. If the shock be severe, and extensively diffused over the 

 body, the contraction slowly extends to the whole mass ; the most 

 violent local injury, indeed, seems to be totally unperceived at re- 

 mote parts of the body : whilst a general shock, such as striking the 

 vessel which contains the expanded polyp, produces a simultaneous 

 contraction of the whole.* The polyps, however, exhibit much 

 greater irritability, and their movements, from their rapidity, form 

 a striking contrast to the languid contractions of the connecting 

 central mass ; but that they have a community of life appears im- 

 probable : 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 neighbourhood will likewise not unfre- 

 quently retire, but this circumstance may be accounted for by the 

 sudden movement of their neighbour ; for, as the polyps often touch 

 each other with their tentacles, there is no cause for urging a com- 

 munity of substance to explain it."f" 



(40.) Madreporidce. Were we to imagine one of the alcyonidse 

 capable of secreting not merely the calcareous spicula which are 

 mixed up with the softer portions of its body, but abundant quan- 

 tities of carbonate of lime, which, being stored up in the centre of 

 its substance, should form a dense calcareous axis encrusted with 

 the uncalcified part of the living animal, and perforated at its sur- 



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

 vol. ii. p. 261. 



t Quoy et Gaimard, Zoologie du Voyage de I'Uranie. Paris, 1834. 



