250 COMPARATIVE ZOOLOGY. 



naria in its usually larger size and solid disk, four radiat- 

 ing canals, which ramify and open into a circular vessel, 

 running around the margin of the disk. 129 



CLASS II. Anthozoa. 



These marine animals, which by their gay tentacles con- 

 vert the bed of the ocean into a flower-garden, or by their 



secretions build up coral-islands, 

 have a body like a cylindrical 

 gelatinous bag. One end, the 

 base, is usually attached ; the 

 other has the mouth in the cen- 

 tre, surrounded by numerous 

 hollow tentacles, which are cov- 

 ered with nettling lasso -cells. 

 This upper edge is turned in so 



Fio.m-Horizontal Section of Ac- * S t0 f mi a SaC witllin R SaC > 



tinia through the stomach, show- like the neck of a bottle turned 



ing septa and compartments. 



outside in. The inner sac, which 



is the digestive cavity, does not reach the bottom, but opens 

 into the general body-cavity (Fig. 38). 130 The space between 

 these two concentric 

 tubes is divided by a 

 series of vertical parti- 

 tions, some of w r hich 

 extend from the body- 

 wall to the digestive 

 sac, but others fall 

 short of it. Instead, 

 therefore, of the radi- 

 ating tubes of the Aca- 

 leph, there are radiat- 

 ing spaces. No mem- 

 bers of this class are 



Fia. 199. Actinia expanded, seen from above, 

 All are showing mouth. 



