28 ON POLYPS. 



find sometimes five, sometimes six, or more of these appendages ; 

 but in all the cortical polyps there are eight. The tentacles, also, 

 are not unfrequently pinnated or slightly fringed on each side, but 

 never provided with moveable cilia. The body of the polyp, when 

 withdrawn from its cell, is somewhat globular, and more complex 

 in its structure than that of the hydra. In Jig. 5,2, a diagram is 

 given, representing the Alcyonium exos, in which the following 

 parts may be distinguished. The stomach* is considerably dilated, 

 and terminates inferiorly in a tubular prolongation, b, which ex- 

 tends into the substance of the common mass, into which it most 

 probably conveys nourishment. But the main difference observ- 

 able between the alcyonidse and the hydra consists in the possession 

 of a reproductive organ or ovary, in which the germs of its progeny 

 are developed. This consists of a tubular filament, c, lodged in 

 the cell which the polyp inhabits, which opens by one extremity 

 into the bottom of the stomach, into which the ova when mature 

 are conveyed, and they are ultimately ejected through the mouth, 

 a, as represented in the figure. 



(38.) Few objects exhibit to the naturalist a more beautiful spec- 

 tacle than the compound animals of which we are speaking. When 

 found upon the shore contracted and deformed, it would be diffi- 

 cult to imagine that they were really organized beings, much less 

 possessed of the elaborate conformation we have described ; yet, on 

 placing one of them in a tumbler of sea-water, and watching it 

 attentively with a magnifying glass, its true nature is gradually re- 

 vealed : the central mass expands in all directions, exhibiting the 

 cells upon its surface, from which in time the countless flower-like 

 polyps are protruded, and, stretching out their arms in all directions, 

 wait for the approach of prey. A scene like this naturally leads us 

 to make a few observations upon some points of physiology con- 

 nected with their economy : several questions obtrude themselves 

 upon us, which, although applicable to the whole group of com- 

 pound polyps, may be well discussed in this place. 



(39.) That there is a community of nutrition, or, in other words, 

 that food taken and digested by the individual polyps is appropriated 

 to the support of the general body, appears to be indisputable, and 

 is generally admitted ; but is there a community of sensation so as to 

 render the entire mass one animal, capable of consentaneous move- 

 ments, or is each polyp independent of the rest in its sensations 

 and actions ? Upon this there are different opinions : some regard- 

 * Spix (Jean), Memoire pour servir a I'histoire de 1'Alcyonium exos. 



