ON POLYPS. 



the side of one of these creatures, not only does the wound soon 

 heal, but a young polyp sprouts from the wounded part ; if it be 

 cut into two portions by a transverse incision, each soon deve- 

 lopes the wanting parts of its structure ; if longitudinally di- 

 vided, both portions soon become complete animals ; if even it 

 be cut into several parts, every one of them will rapidly assume the 

 form and functions of the original ; the inversion of its body, by 

 turning it inside out, does not destroy it ; on the contrary, the ex- 

 terior surface assumes the office of a stomachal cavity, and that 

 which was originally internal will give birth to buds, and take 

 upon itself all the properties of the skin. 



(35.) Cortical compound Polyps. From what we have said con- 

 cerning the two preceding families of polyps, one composed of 

 animals consisting entirely of a gelatinous crust which invests a fixed 

 and immoveable skeleton ; the other exhibiting active and hungry 

 creatures, provided with an internal digestive cavity, and endowed 

 with the capability of seizing and devouring living prey, we are 

 prepared to examine the more complex structure of compound 

 polyps, which combine in themselves the characteristics of both 

 families. The compound polyps consist of a mass of gelatinous 

 matter, which indicates, by its power of contraction upon the appli- 

 cation of stimuli, a degree of sensation ; and of a great number of 

 hydrseform polyps, which spring from the surface of the common 

 body, and are individually capable of seizing and digesting prey, 

 the nutriment thus gained being appropriated to the nourishment of 

 the general mass. The animals of this division are provided with 

 numerous mouths and stomachs, each endowed with a power of 

 independent action. 



Although essentially similar in their habits, the compound 

 polyps present various modifications of structure, which natu- 

 rally leads them to be grouped in distinct families. Some- 

 times the central common mass is entirely soft and gelatinous, 

 its surface being covered with minute cells in which the polyps 

 are lodged; such are the Alcyonidas. Sometimes the common 

 body secretes large quantities of calcareous matter in the same man- 

 ner as the Fungia, which, being deposited in its interior, forms 

 arborescent masses, presenting upon their surface multitudes of 

 cells, generally distinguishable after the removal of the outer 

 crust, in each of which when alive a polyp existed : these form 

 the family of Madrepores. The central axis is not unfrequently 

 quite solid and smooth upon the surface, offering no cells for the 



