34 ON POLYPS. 



diffused through the cortex, which not unfrequently is likewise 

 gorgeously coloured by secretions of different hues. In the Gor- 

 goniae, a section of one of which (Gorgonia verrucosa) is repre- 

 sented in Jig. 7, A, the earthy matter in the crust is so abundant, 

 that, even when dried, it will retain in some measure its natural 

 form, and exhibit the tints peculiar to the species. 



The structure of the individual polyps of the Corallidse, as far 

 as we are acquainted with their history, resembles that of one 

 of the polyps of the Alcyonidse already described ( 36) ; and the 

 prey obtained by each, goes to the support of the general mass. 

 Their reproduction is undoubtedly from germs developed in in- 

 ternal filamentary ovaria, which escape either through the mouth, 

 as in Alcyonium, or else, as Cavolini* supposed, through apertures 

 placed between the origins of the tentacles. 



(47.) Pennatulidce. This family belongs likewise to the divi- 

 sion of cortical polyps, and agrees with the two last in most points, 

 the principal distinction consisting in the character of the internal 

 axis which supports the body. In some species this part is reduced 

 in fact to a ligamentous mass, interspersed with calcareous granules ; 

 but, in the most typical forms, the skeleton consists of several 

 pieces, capable of moving upon each other. The whole animal, 

 in such cases, resembles a feather, the stem supporting lateral 

 branches, upon which the polyps are arranged. From the circum- 

 stance of these compound animals being unattached to any foreign 

 support, they have been supposed to be capable of swimming at 

 large in the sea, by the voluntary movements of their articulated 

 branches, a fact strongly contested by many modern zoologists ; 

 but, as we can say nothing from our own observation upon this 

 subject, we must leave the question open to future investigation. 

 Many species are eminently phosphoric. 



Tubiporidcc. We now have to speak of a class of polyps very 

 different in their construction from those which have been described. 

 Instead of encrusting an internal solid skeleton, the Tubiporidse are 

 enclosed in a calcareous or coriaceous sheath or tube, from the ori- 

 fice of which the polyp is protruded, when in search of prey : these 

 are named by authors Vaginated Polyps. 



(48.) The Tubipora musica (jig. 8, a) is the species which has 

 been most carefully studied, and the details connected with its or- 

 ganization will be found of the highest importance, as affording a 



* Cavolini (Philippe), Memorie per servire alia storia diPolipi marini. 4to. Naples, 

 1785. 



