ZOANTHARIA. 



177 



A. ZOANTHARIA MALACODERMATA. Though, from their 

 soft nature, unknown in a fossil condition, the Sea-anemones 

 merit a brief description here, as they may be taken as the 

 types of the order, and as the somewhat complicated struc- 

 ture of the sclerodermio coral will thereby be rendered much 

 more intelligible. 



Fig. (37. A, Actinia mesembryanthemum, one of the Sea-anemones (after Johnston) ; B, Section 

 of the same, showing the mouth (a), the stomach (6), and the body-cavity (c). 



The body of a Sea-anemone (fig. 67) is a truncated cone, 

 or a short cylinder, termed the " column," and is of a soft, 

 leathery consistence. The two extremities of the column are 

 termed respectively the " base " and the " disc," the former 

 constituting the sucker, whereby the animal attaches itself at 

 will, whilst the mouth is situated in the centre of the latter. 

 In a few cases (Cerianthus and Peachia) the centre of the 

 base is perforated, but the object of this arrangement is 

 unknown. Between the mouth and the circumference of 

 the disc is a flat space, without appendages of any kind, 

 termed the " peristomial space." Round the circumference 

 of the disc are placed numerous tentacles, usually retractile, 

 arranged in alternating rows, and amounting to as many as 

 200 in number in the common Actinia. The tentacles are 

 tubular prolongations of the ectoderm and endodeim, con- 

 taining diverticula from the somatic chambers, and sometimes 

 having apertures at their free extremities. The mouth leads 

 directly into the stomach, which is a wide membranous tube, 



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