ASTERIAS. 69 



how they are held? With a hand-lens examine around the bases 

 of the spines, and see the arrangement of the pedicellarice. Their 

 function is obscure, but they enable the starfish to hold small 

 objects firmly and they may be of service in dealing with possi- 

 ble surface parasites. 



6. Remove some of the pedicellarice with a scalpel and ex- 

 amine them under the microscope. Do you find more than one 

 kind? 



Draw a pedicellaria. 



Internal Structure. Make the dissection under water, and in 

 cutting through the integument be careful not to injure the 

 underlying soft parts. 



With strong scissors cut through the aboral body-wall near 

 the tips of the rays of the trivium. Carry the cuts forward 

 along the sides of the rays to the disk. The cavity thus opened 

 is the coelom or body cavity. 



Lift up the integument at the tip of each arm and carefully 

 snip away the mesenteries which attach the organs to it. Cut 

 the membranes that extend into the disk opposite the junc- 

 tions of the arms, and remove the three-rayed flap of integu- 

 ment thus freed, cutting as close as possible to the madreporite, 

 but leaving this in place. 



Digestive System. In studying this system you should con- 

 stantly bear in mind the peculiar method by which the animal 

 feeds, as the digestive system is highly modified to suit this 

 method. 



1. The short, cone-shaped intestine and the intestinal cceca 

 were probably removed with the integument. The intestine 

 probably does not function, and may be regarded as a vestige. 

 It opens near the center of the disk, on the aboral side, by a 

 very minute anus that is very hard to see. 



2. The stomach, which occupies the greater part of the space 

 in the disk, is composed of a small aboral portion, the pyloric 

 division, that receives the ducts from the hepatic caeca, and a 

 larger, lobed, cardiac division, into which the mouth opens. 

 The cardiac portion may be everted through the mouth, thus 

 being turned wrong side out. Five pairs of muscles, which draw 

 this portion of the stomach back into place, may be seen at' 



