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 caeca 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 disc, on the aboral side, by a very minute anus 

 which is hard to see. 



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

 within the disc, 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 attached to the ridges formed 

 by the ambulacral plates in each arm. 



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

 caeca. The ducts from each pair unite and join the pyloric division 

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

 What reason is there for ten enormous digestive glands? Does 

 this have anything to do with the method of feeding? 



Make a drawing of the digestive system of the disc and of one arm. 



II. REPRODUCTIVE SYSTEM. 



Turn the hepatic caeca to one side and note the ovaries or testes. 

 The sexes are separate, but the gonads 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 caeca. 

 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 in one arm of your figure. 



IV. WATER- VASCULAR SYSTEM. 



i. Carefully remove the side of the stomach next to the bivium. 

 being very careful not to disturb the stone canal, which runs from 

 the madreporic plate to the margin of the membrane about the 

 mouth. By the side of the stone canal is a thin band of tissue 

 formerly supposed to be a heart. It is now generally believed to 

 be connected with the reproductive system, and is commonly referred 

 to as the axial organ. It has nothing to do with the system now 

 under consideration. 



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