Coelenterata. 



175 



secreted by the common body substance, or cenosarc, connecting 

 the individual polyps. 



Imagine the sea anemone depositing limy matter in the base 

 of its body wall, forming a cup ; fleshy radial ridges rising from 

 the floor and wall of the cup between the mesenteries, and a 

 similar deposit in these ridges ; thus it will be seen how the cup 

 is formed by the individual polyp. By the continued growth of 

 the polyp, and the continuation of the limy deposit, the cup be- 

 comes an elongated tube. By budding are formed the branches 

 of these tubes, increasing in size and in the number of partitions 

 as they grow. 



4. Between the cups, a porous secretion of the same material 

 as that in the cups. This is deposited in the common fleshy 

 base, filling up, in some forms, the spaces between the cups ; and 

 when one polyp dies, its cup is covered over and buried out of 

 sight by this secretion of the common base. 



5. Make a drawing of a mass of stony coral, showing the gen- 

 eral arrangement of the cups, their mode of branching, and the 

 common secretion between them. 



6. Draw a cup as seen from its free end. Make also a draw- 

 ing of a cross section of the same cup toward the smaller end. 



In the stony corals the mesenteries are always in pairs, and the 

 fleshy ridges, in which are secreted the septa, arise between 

 them. 



The tentacles are generally in multiples of six, and are not 

 fringed. It is of this kind of coral that the reefs are formed. 



SEA FEATHER, OR SEA FAN. 



In a sea feather, e.g., Muricea, note : 



i. An outer barklike layer; with the thumb nail scrape off a 

 little of this layer and pulverize it between the thumb and 

 finger ; mix this powder with water and examine under a micro- 

 scope. A better way to see the spicules is to clean them thor- 

 oughly by boiling some of the outer layer in caustic potash. In 

 this layer are holes from which the polyps protruded. In this 



