55 



surface of this stony skeleton was incrusted with a layer of animal 

 jelly, dipping down into the interstices of the plates, and covering the 

 whole framework. In the figure, the darker portion indicates the 

 living crust.; whilst from the lighter parts it has been removed, to 

 show the stony skeleton itself. There are no arms or moving parts 

 adapted to the prehension of food, and no separation of organs for the 

 performance of the vital functions ; the thin membranous film apparently 

 absorbs the materials of its support from the water of the ocean, and 

 deposits within its substance the calcareous particles which it secretes, 

 moulding them into the form peculiar to its skeleton, which it gradually 

 enlarges as its own extent increases. 



(115.) The gelatinous investment, however, gives certain dubious 

 indications of vitality, and possesses a power of contraction so as to 

 retire between the laminae of its skeleton when roughly handled, and 

 thus conceal itself from injury. Upon the surface of the soft crust are 

 seen a number of vesicles (indicated in the figure), which have been re- 

 garded as rudimentary tentactila from the circumstance of their being 

 able to contract and vary their dimensions ; recent observations, how- 

 ever, lead to the belief that they are cavities filled with air, serving an 

 important purpose in the economy of the creature namely, that of 

 preventing it from being turned upside down by the occasional agitation 

 of the ocean. These air-vessels may therefore be looked upon as floats, 

 which, rendering the upper surface more buoyant than the inferior, 

 materially assist in preventing such an accident. 



(116.) The reproduction of Fungia is effected by the development of 

 sprouts or gemmae which pullulate from the animal substance as buds 

 issue from a plant, and remain for some time fixed to the parent by a 

 species of foot-stalk, which sustains them until they have attained to 

 a considerable size, the young Fungiae being upwards of an inch in 

 diameter before they become detached. When mature, they separate 

 from the top of the stony peduncle which hitherto supported them ; 

 and at this time the skeleton of the young Fungia, when divested of 

 its fleshy part, shows a circular opening beneath, through which the 

 radiating plates of the upper surface are visible. In a short time a 

 deposit of calcareous matter takes place, which cicatrizes the opening, 

 the marks of which, however, can be traced for a considerable period. 



(117.) In the earliest period of its development, the foot-stalk by 

 Which the young is united to the parent, as well as its radiating disk, is 

 entirely enveloped with the soft parts of the animal ; but as the upper 

 portion spreads, and assumes its characteristic form, the pedicle is left 

 naked, and the gelatinous coating extends only to the line where the 

 separation afterwards takes place. 



(118.) It is generally supposed that the calcareous matter forming 

 the skeleton of these madrepores is perfectly external to the living 

 crust that secretes it, and accordingly is absolutely extra-vital and 



