72 ECHINODERMATA. 



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 cseca, 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^ 

 tached to the ridges formed by the ambulacral plates in each arm. 

 How is it possible for the stomach to be everted ? What reason 

 is there for two divisions? 



3. In each arm is a pair of long, glandular organs, the hepatic 

 cceca. The ducts of each pair unite and join the pyloric divi- 

 sion of the stomach by a common duct. These are digestive 

 glands. What reason is there for having ten enormous digestive 

 glands? Does this have anything to do with the method of feed- 

 ing? 



Make a drawing of the digestive system of the disk and one 

 arm. 



Reproductive System. — Turn the hepatic cseca to one side and 

 notice the ovaries or testes. The sexes are separate, but the 

 organs have the same general appearance in both sexes. They 

 vary in size according to the season of the year, sometimes 

 being so small that they are not easily found, and again being 

 nearly or quite as large as the hepatic cseca. With a pair of 

 forceps lift up one of these organs and see where it is attached. 

 It is at this point that the reproductive cells reach the exterior. 

 How many gonads are there ? 



Draw the gonads into another arm of your figure. 



