34 Invertebrate Zoology. 



madreporic plate, and is directly comparable with the same 

 of the starfish. Arranged between the genital plates, and 

 consequently at the apex of the ambulacral areas, are the 

 five small ocular plates. 



Make drawings of the animal as seen from above and from 

 below, naming the parts ; also make enlarged drawings of a 

 spine with its " ball and socket " joint and of a pedicellaria. 



Remove the spines and thoroughly wash the shell. The 

 ambulacral and inter-ambulacral areas will be clearly shown. 

 Find the openings through which the ambulacral suckers 

 may be thrust out. What is the arrangement of these open- 

 ings, the ambtdacral pores ? 



Make a drawing of the denuded shell. 

 ,/ 

 Tiie Digestive System. Around the margin of the 



mo'iith the five hard teeth will be observed. With a pair 

 of" scissors carefully remove the membranous peristome and 

 wash out the body-cavity with clean water. The esophagus, 

 after passing through the complicated dentary apparatus, 

 inclines to the wall of the shell, where it passes into 

 the somewhat enlarged and elongated stomach. Break- 

 ing the shell if necessary, follow the course of the ali- 

 mentary tract to the anus, noting any mesentery that may 

 hold it in place, and observing the structure of its free 

 border. 



By a diagram illustrate the course of the alimentary tract. 



The Reproductive System. The sexes are separate, 

 though, as in the starfish, the sexual glands superficially 

 resemble each other. The glands appear as five radially 

 arranged masses, and are closely attached to the perivisceral 

 walls. Each gland opens to the exterior through the pore 

 already noted in the genital plate. 



