no ELEMENTARY ZOOLOGY 



Make a drawing of the aboral surface showing all these 

 parts. 



On the oral surface note the centrally-located mouth, 

 the ambulacral groove 's, one running longitudinally along 

 each ray, and in each groove two double rows of soft 

 tubular bodies with sucker-like tips. These are called 

 the tube-feet and are organs of locomotion. Make a 

 drawing of the oral surface. 



Internal structure (figs. 18 and 19). TECHNICAL NOTE. 

 Take a specimen which has been immersed for some time in the nitric 

 acid solution, and with a strong pair of scissors, or better, bone- 

 cutters, cut away all the aboral wall of the disk except that immedi- 

 ately around the madreporite and the anus. Now begin at the tip 

 of each ray and cut away the aboral wall of each, leaving, however, 

 a single arm intact. When the roof of each arm has been carefully 

 dissected away the specimen should appear as in fig. 18. 



Note the large alimentary canal, which is divided into 

 several regions. Note the short cesophagus leading from 

 the mouth on the oral surface directly into a large mem- 

 branous pouch, the cardiac portion of the stomach. By 

 a short constriction the cardiac portion is separated from 

 the part which lies just above, i.e., the pyloric portion of 

 the stomach. From the pyloric portion large, pointed, 

 paired glandular appendages extend into each ray. 

 These are the pyloric cceca. Their function is digestive, 

 and oftentimes they are spoken of as the digestive glands 

 or "livers." The pyloric caeca, as well as the cardiac 

 portion of the stomach, are held in place by paired muscles 

 which extend into each arm. Note two sets of these 

 muscles, one set for thrusting the cardiac portion of the 

 stomach out through the mouth and another for pulling it 

 back, the protractor muscles and retractor muscks, 

 respectively. The starfish obtains its food by enclosing 

 it in its everted stomach and then withdrawing stomach 

 and food into the body. Note that the pyloric portion of 

 the stomach opens aoove into a short intestine terminating 



