ORDER ACTINOIDEA. 47 



Here belong the Actinias and the Zoanthidae, and a large part of coral 

 animals. The Zoanthidse are closely related to one division of the 

 coral-making Caryophyllacea — the family Gemmiporidse. They 

 spread a wide disk, with a somewhat convex centre, and some- 

 times the margin of the disk, bearing the fringe of tentacles, becomes 

 much reflexed by expansion, curving downward towards the base of 

 the polyp, so as to appear like a cap over the extremity. The tenta- 

 cles are short, and correspond each to a radiate line on the disk ; and 

 in some species I have found one of these rays to have a different 

 colour and size from the others, evincing some peculiarity of function 

 in the tentacle, corresponding, apparently, to the long finger-tentacle 

 in some madrepores. The Gemmipores* resemble these in general 

 form and in their fringe of short tentacles, but the disk is not striated. 

 In another division of the Caryophyllia tribe — the Caryophyllidaa — 

 the tentacles are much like those of the common Actinia; and in ex- 

 ternal form we distinguish no important peculiarity, except that the 

 disk containing the mouth becomes more prominent, when the animal 

 is fully expanded, t sometimes having nearly the shape of an oblong 

 inverted cone. 



The polyps of the Astraa tribe of zoophytes have numerous unequal 

 tentacles, and a flat or simply convex disk. The distinction between 

 the Astrsea and Caryophyllia tribes depends on a different mode of 

 budding, as is pointed out in a following chapter. The visceral 

 lamellfe in the Astrreas appear to retain their identity through the 

 side tissues or walls of the polyp, and, in compound species, these 

 lamellae may be traced by their secretions through the intermediate 

 spaces between adjoining polyps. These characters are strongly 

 marked in the coralla of the different animals, although not so appa- 

 rent, as far as I have examined, in the recent Actiniae (H 48 and 76, 

 fig. 34). 



43. The only variation from the Actinia type which we here notice 

 is presented by the Fungioe and other allied zoophytes. The Fungiaaf 

 are the largest of known polyps, some species attaining a diameter of 

 eighteen inches. The form of the animal, instead of being cylin- 

 drical, as in the Actinia, is that of a large disk, an inch or two thick, 

 circular or elliptical in outline, and either flat or convex above. A 

 large oblong mouth occupies the centre, and from the mouth narrow 

 ridges radiate, with regular intervals, to the circumference — a few 



* See plate 30, figure 4. t Plate 27, figure 1. $ See plates 18 and 19. 



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