THE STARFISH 121 



ony. The harder parts of the coral are secreted by the ecto- 

 derm, but in some kinds as the sea fan and red coral, an 

 additional layer of loosely connected particles of carbonate 

 of lime is secreted in the mesogloea. 



THE STARFISH 

 Asterias sp. 



General Suggestions. — The starfish is the best repre- 

 sentative of this branch for laboratory study. Specimens 

 may be obtained from any of the supply laboratories, and 

 may be kept in two per cent, formalin or seventy per cent, 

 alcohol for an indefinite period. Dried specimens may be 

 made to serve the purpose of this study if soaked for a 

 while before using in hot water. A few specimens with 

 water vascular system injected should be obtained with 

 the others, and kept on hand for reference. 



If possible a few specimens of sea urchins and sea cu- 

 cumbers should be on hand for comparison. 



Dried Specimen. — (i) Examine the specimen as a 

 whole. Note its shape, length of arms, and differences be- 

 tween the two sides. 



(Each arm is a ray, the sides are oral and aboral, the 

 central body is the disk.) 



(2) Note the covering of the aboral side. Remove one 

 of the spines, examine it carefully as to length, attachment, 

 and size. 



(3) Note the arrangement of the spines on the oral and 

 aboral sides. Find between two of the arms on the aboral 

 side an oval plate covered with radiating grooves; this is 

 the niadreporic body. Examine and draw the aboral side 

 (X/2). 



