174 PRACTICAL ZOOLOGY. 



the individual polyp. By the continued growth of 

 the polyp, and the continuation of the limy deposit, 

 the cup becomes 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 ma- 

 terial 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 general 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 

 drawing 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 bark-like 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 microscope. A better way to see 



