[2 ORGANS OF SUPPORT, 



fleshy crust penetrates to a considerable extent the loose, 

 porous surface of the calcareous mass, from which it is 

 capable of receiving some protection, and consequently we 

 perceive distinct indications of the positions of the polypi 

 on the surface of the skeleton in these animals. These cells, 

 for the protection of the polypi, have generally a radiated 

 lamellar structure, and vary remarkably in their size and 

 also in their form in different lithophytes. They are very 

 minute in the porites, larger in the madrepores, still larger in 

 the caryophyllia, and the fungia agariciformis forms but 

 one enormous cell for the lodgment of a polypus like an 

 actinia. 



In some of the lithophytes the fleshy crust, as in the cortical 

 kinds of keratophytes, is of great thickness, and the polypi 

 developed from this fleshy exterior mass leave no indications 

 of their position on the surface of the internal calcareous 

 axis. This is seen in the common red coral, which is a solid 

 internal calcareous skeleton, striated with superficial lon- 

 gitudinal grooves, but presenting no calcareous cells for the 

 polypi, which are protected solely by the fleshy thick 

 covering of which they form parts. In the agaricm, mean- 

 drinte, and many others, we observe a laminated general sur- 

 face of the skeleton for the protection of the fleshy mass, 

 but no distinct cells for the polypi. In the virgularm the 

 skeleton consists of a straight internal calcareous solid 

 cylindrical pillar, occupying the longitudinal axis of the body, 

 and protruding from the lower part of the animal. In the 

 pennatula the internal calcareous axis is soft and flexible at 

 its extremities, from the abundant proportion of glutinous 

 matter in its composition, and to allow of the necessary con- 

 tractions and extensions of the animal's body in a longitudi- 

 nal direction. In the isis the internal solid calcareous 

 skeleton is jointed at regular and short distances throughout 

 the whole body, and there are no external cells for the 

 polypi, which are entirely confined to the thick fleshy crust 

 which covers the entire animal in the living state. The 

 joints here consist of the same glutinous tough matter which 

 pervades the whole calcareous axis, and are only uncalcified 

 portions of the general solid axis. They are formed by con- 

 centric layers, like the calcified solid portions of the skeleton, 

 and they allow of considerable flexion in the branches and 

 stem of this delicate ramified, and highly organized animal. 



