C(ELENTERATA. 



173 



ORDER II. HEXACORALLA. 



As the name indicates, the septa and tentacles here 

 occur in multiples of six. Here belong all the sea-anem- 

 ones and the true corals, which produce coral-reefs and 



*^^^ f ^-\^3 

 f fj&%s&*%sA ^!^?JTO 





FIG. 20. Sea-anemone (Metridium). From Emerton. 



islands. The reef -building species are limited in their 

 distribution by temperature, for they cannot live where 

 the temperature of the water falls below 60 Fahr. (13 C,). 



SUBCLASS II. SCYPHOMEDUS/E (Jelly-fishes). 



At first sight the Scyphomedusse differ greatly from 

 the Actinozoa. They are free-swimming forms (medusa?) 

 in which the body is umbrella-shaped, the mouth is at the 

 end of a proboscis, and all is semitransparent. Yet when 



