Invertebrata. 



FIG. 25. 



CHAPTER VIII. 



ACTINOZOA. SUB-CLASS I. ZOANTHARIA : SEA 

 ANEMONES. 



Struct'ire of a Sea Anemone. In many of the 

 rock-pools around our shores there are to be found 

 the exquisite forms which are the types of this 

 class, and which, like animated flowers, may be 

 seen expanding their sensitive petal-like tentacles 

 in search of the materials that constitute their prey. 

 On the retreat of the tide those that are left un- 

 covered by the water contract, and appear as little, 

 rounded, firm, gelatinous masses, attached to rocks 

 and stones by means of a flat suctorial disk. 



The body of one of 

 these when expanded is 

 somewhat cylindrical, hav- 

 ing a free extremity which 

 bears the mouth, and an 

 attached end, which is 

 usually capable of volun- 

 tary detachment. This 

 extremity is sometimes 

 called the foot. On mak- 

 ing a transvqrse section 

 the body appears like a 

 double tube ; the outer 

 tube is the body wall, the 

 inner bounds the stomach, 

 body-cavity into which the 

 by a narrow aperture. 



Vertical section of common Sea ane- 

 mone, Actinia uiesembryauthe- 

 uiiim. 



in mouth, m' primary mesentery 

 m" secondary mesentery, e ecto- 

 derm, e 1 endoderm, t tentacle, /', 

 ovary, d disc of attachment, f 

 body-cavity. 



and between them is the 

 stomach-sac opens below 



