34 



ZOOPHYTES. 



Fig. 14. 



Fig. 13 b. The coats of the stomach, in this species, contain the 

 same ra i nute spicules as the tentacles; and, in the general 

 integuments of the body, they are still more abundant. 



The visceral cavity is divided vertically by numerous 

 lamellae attached to its walls, the larger of which are united by their 

 inner margin to the exterior of the stomach, and serve to fix it in 

 its place, and at the same time to vary its shape by their muscular 

 action. This structure is exhibited in the annexed cut of an ideal 

 transverse section through the centre of an Ac- 

 tinia. The central ring is a section of the sto- 

 mach, exterior to which the radiating lamellae are 

 shown of various sizes. All the lamellae, large 

 and small, extend along the under surface of the 

 disk to the stomach ; but only certain lamellae 

 at intervals retain this width and continue con- 

 nected with the stomach to its lower extremity ; 

 the greater part narrow at once, and are of va- 

 rious widths, as in the figure annexed. Below the stomach, the 

 larger lamellae also are abruptly narrowed, so as to leave here an 

 open space or chamber ; the lamellae afterwards extend inward again 

 along the base of the polyp, and coalesce at centre, or are lost in the 

 general structure of the base. The cavity or visceral chamber below 

 the stomach is sometimes nearly bisected by the union of opposite 

 lamellae. 



In the Actinia marginata, the lamellae, as seen through the skin, 

 have the arrangement in figure 15, two stouter lamellae 

 with a broader interval alternating with two thinner 

 lamellae and three narrower intervals. The same fact is 

 indicated by the vertical linings on the Actinia, figure 22, 

 plate 3 ; and, from some facts hereafter to be stated, it will 

 be shown to be a very common arrangement in these animals. The 

 vertical markings of Actiniae, as well as the radiations of the disk, are 

 all connected with the position of the fleshy lamellae within. The 

 above figure also shows that these lamellae are very numerous, six 

 or seven being included in a breadth of a quarter of an inch. They 

 are not as distant as in figure 14, which is drawn for general illustra- 

 tion, and is not strictly accurate. 



The number of lamellae in a certain breadth of interval is the same 

 in different individuals of the same species. As a polyp enlarges by 

 growth, new lamellae form between the others, in the widening inter- 



Fig, is. 



