148 ACTINOZOA. 



the latter, runs a tube occupied by a number of 

 granular bodies, and giving off, at right angles to 

 itself, a series of short vertical branches, which 

 open along the line of the locomotive fringes to 

 communicate with the surrounding medium. 



4. Prehensile apparatus. — The tentacles of 

 the Actinozoa, like those of the Hydrozoa, appear 

 usually, if not always, as hollow appendages, in 

 immediate connection with the somatic cavity, 

 their walls being richly provided with thread-cells 

 and consisting throughout of two layers, an ecto- 

 derm and an endoderm. 



Among the Zoantharia, the tentacles vary ex- 

 ceedingly in size and external form. Viewed from 

 without, they are seen to arise, save in Emnenides, 

 from the distal extremities of the polypes, 

 between the mouth and the outer margin of the 

 disc {figs. 33 — 35). Dissection shows them to be 

 hollow processes in free communication with the 

 somatic chambers, each of which is furnished with 

 one or more of these appendages. Their most usual 

 form is that of a slightly curved, more or less 

 tapering, cone, as in many species of the genus 

 Actinia itself. But from this typical aspect there 

 are very many aberrant modifications. 



Among the Alcyonaria, the tentacles are com- 

 paratively short, closely arranged in a single cycle 

 of eight around the mouth of each polype, their 

 margins being produced into a number of lateral 

 pinnae {fig. 26, a). These last, according to Dana, 

 are perforate at their free ends, the extremity of 

 the tentacle itself being csecal ; but this statement 

 is denied by Milne Edwards and others, who more 

 correctly view the pinnae, in some genera at least, 



