^6 Laboratory Guide in Zoology 



III. — With a pocket lens observe quite carefully the ap- 

 pearance of the rough dorsal and lateral surfaces. Find 

 as many kinds of projections as you can. The hard- 

 pointed projections, or spines, are developments of the 

 body wall, and are used for purposes of protection. 

 Around the bases of the spines are the forceps-like 

 pedicellarise. 



IV. — The soft blunt projections are hollow processes of the 

 body wall. They allow the fluid of the body cavity — 

 visceral fluid — to come into contact with the external 

 water and air, and are called papulae or respiratory coeca. 



V. — Find a small anal opening, lying near the centre of the 



dorsal disk on a line drawn from the centre of the 

 disk to the angle formed by two rays. 



VI. — Place the animal upon its back, and observe its ven- 

 tral surface. Notice the five grooves, one in each ray, 

 terminating internally at the side of a pentagonal- ' 

 shaped depression. Because these grooves contain 

 organs of locomotion they are called ambulacral 

 grooves. 



VII. — Notice that beneath this pentagonal-shaped depres- 

 sion a colorless membrane with a small opening in its 

 centre is stretched. This is the peristome, and the 

 opening in the peristome is the mouth. The peristome 

 is connected with the wall of the alimentary canal. 



VIII. — Observe the kind of organs that fill the ambulacral 

 groove. They are short, cylindrical structures called 

 ambulacra or tube feet. How many rows in each groove ^ 

 The tube feet are a part of quite a complicated system 

 which serves the function of locomotion and possibly 

 of respiration. 



IX. — ^Vith the forceps, push aside the two inner rows of 

 tube feet, so that you can look down into the very roof 



