88 ZOOLOG Y DIIiECTIONS 



3. Examine madreporite with hand lens. Draw. X5. 



4. For convenience of description, the two rays between 

 which the madreporite is located are termed the hivlum, while 

 the remaining three are the trivium. The central ray of the 

 trivium (the ray directly opposite the madreporite) is called the 

 anterior ray. 



5. Place a specimen, ahoral surface uppermost, in suffi- 

 cient water to cover it. The small, soft projections which cover 

 the body wall between the spines are the gills. Each gill is a 

 hollow finger-like process whose cavity is directly continuous 

 with the body cavity. Sea water bathing the outer surface of 

 the gills provides the means of respiration, for the gills and the 

 body cavity are filled with the body fluids. 



6. The pediceUariae, small pincer-like organs, protect the 

 animal, and especially the gills, from injury and remove debris. 

 They are especially abundant about the bases of the spines. Find 

 them. Examine a prepared slide of pediceUariae under the mi- 

 croscope. Find and draw two distinct kinds. In the larger type 

 the basal portion is a distinct piece upon which the two jaws are 

 hinged while in the smaller type the basal parts of the two jaws 

 cross over each other like the handles of a pair of shears or 

 tongs. 



7. A line drawn from the center of the disc along the 

 middle of an arm is a radius. One drawn from the same point 

 exactly between two arms is an inter-radius. Do all radii inter- 

 sect similar parts. All inter-radii? Are radii or inter-radii 

 marked in any way on the aboral surface of animal? Notes 

 required. 



8. Make an outline drawing of the aboral surface show- 

 ing details on the disc and a portion of one ray only, 



9. With the oral surface uppermost notice : — 



The mouth. Position? Size? Is its margin smooth or 

 rough? Note the clusters of spines projecting over it. Are 

 they radial or inter-radial ? 



