136 NATURAL HISTORY OF 



ACTINOZOA (ANTHOZOA). 



I. ZOANTHAKIA. 



Description. 



The Zoantharia or sea-anemones are animals very 

 different in appearance from those already noticed, 

 being all visible to the naked eye, and sometimes 

 attaining a considerable size. They are often exceed- 

 ingly beautiful in colour ; and an observer, seeing 

 them with fully extended disc and tentacles, has diffi- 

 culty in persuading himself that he is not looking at 

 some highly variegated specimens of the floral world. 

 But flower-like as they are, their structure and habits 

 are essentially animal. They diff'er from the hydrozoa 

 in the facts, that the mouth does not open directly 

 into the body cavity, and that the reproductive elements 

 are borne along the margins of septa which divide the 

 body cavity into compartments or chambers. 



A sea-anemone (see Plate XI. figs. 1, 2) may be de- 

 scribed as an animal having a body of a more or less 

 columnar shape, terminated at the lower extremity 

 by the base or pedal disc and at the upper extremity 

 by the oral disc (di). The pedal disc is sometimes 

 scarcely defined, the columnar body gradually tapering 

 at the base ; but the oral disc is always distinct. The 

 oral disc bears the tentacles (t), which are extensions 

 of the body wall, and communicate directly with the 

 body cavity. In the centre of the oral disc is the 

 mouth (m) opening into the oesophagus (oes), which 

 is grooved, and hangs from the sides of the mouth 



