40 



Lessons in Zoology. 



Fig. 5. 



Fig. 5 is a diagram rKpiesenting a cat throngh a aea-nrohin ; s ia 

 the sieve, or madreporic body, and c the tuhe leading from it to t.he 

 riog aronnd the mouth, from whioh 

 branoh the five radial water-tnbes 

 (/'). Each of these radial water- 

 tabes connects with the sacs (g) of 

 the tabe-feet and ends in a single 

 tnbe-foot (x), whioh passes ont 

 through an eje- opening. The black 

 line oatside of / is a radial nerve, 

 also oontinaous with a cord aronnd 

 the month. The ont ends of the 

 intestine are seen at i!;; the ovaries 

 at I. ; the branchial tnfts at m ; at h, 

 the teeth; and at i, some of the 

 mnacles that move the jaws ; i is a 

 spine ; e, a plate of the shell ; and n, one of the forks, or pedi- 

 oellarias. 



If any of the children have sand-dollars (Fig. 6) or 



sand-cakes, as they are 

 often called, they will be 

 delighted to discover that 

 they are simply flattened 

 sea-urchins. Perfect ones 

 are very pretty, with their 

 mouse-colored covering of 

 tiny spines, and the bare 

 shells show the different 

 rows of plates and the 

 mouth on the under side. 

 The tube-feet project from 

 perforated plates, and form the beautiful star on the back 

 by expanding into gill-like appendages. This sea-urchin 

 lives partly buried in the wet sand of our shores and of 

 the shallow waters. 



ma 6. 



