248 



HIGH SCHOOL ZOOLOGY. 



Kg. 182.— Diagram of Actinia 

 (From Ludwig). 



a, tentacle ; b, piouth ; e, stomach- of COral-reefs. 

 sac ; d, its opening into coelenteron 1 ; 

 e, septum ; e ' , secondary septum ; f , g, 



apertures in septum ; h, muscular 



slips ; i, reproductive organs k, mes- • 

 enteri al filaments. 



selves. In the lattei* case, it may 

 be only in the form of detached 

 calcareous spicules, but oftener 

 the sjjicules unite into a con- 

 tinuous structure, which pene- 

 trates the wall alone (Tubipora, 

 Fig. 184) or even the septa of the 

 polyps, forming thus a " cup-coral " 

 (Fig. 185). Abundant fossil ex- 

 amples of such cup-corals occur 

 in the Palaeozoic strata of Ontario, 

 but the living representatives of 

 the group are chiefly confined to the 

 warmer seas of the present day, 

 where many species contribute to 

 the formation of the different kinds 



v — 



Fig. 183. — Red coral. (Corallium ruhrum). 

 P, the calcareous axis or sclerobase. A, coenosarc investing the axis and contain- 

 ing the individual polyps, B, these are in different stages of retraction ; d, tentacles ; 

 OB, stomach-sac ; ni, missenteries. The ccenosarc is cut through and turned back, so as 

 to show the canals (1 and n) which traverse it, and the axis which it co\ers. 



