94 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



7. On the side of the upper end of the stone canal 

 notice a small dark brown corrugated pouch, the heart. 



e. Cut the stone canal, and separate the wall of the 

 intestine from the wall of the oesophagus, and turning the 

 periproct to one side, trace the course of the digestive 

 tract, noticing : 



1. The intestine, (Fig. 39, d), running downwards 

 from the anus, and passing through one of the repro- 

 ductive organs, underneath which it joins the " pyloric " 

 chamber of the stomach. 



2. This is a long, flat, wrinkled brown tube,y, which 

 runs around nearly the whole circumference of the body. 

 Its inner or central edge is free, but its outer edge is 

 attached to the integument on each side of each ambu- 

 lacral area. Notice the small, lighter-colored vessel which 

 runs along its inner or free edge. After running around 

 the body, it bends down upon itself to join the " cardiac " 

 chamber (Fig. 39, g). 



3. This also runs almost entirely around the body, but 

 in the opposite direction. Its outer edge is folded or sac- 

 culated, and is attached by mesenteric membranes to the 

 integument on each side of each ambulacra! area, while 

 its inner margin is free, and bounded by a large, smooth- 

 walled tube, which is sharply distinguished from the outer- 

 sacculated portion. After encircling the body, the car- 

 diac chamber bends upwards to join the oesophagus, e. 



4. This is a somewhat smaller tube, which makes two 

 abrupt bends upon itself, and then passes up on to the 

 ab-oral surface of the lantern to enter the channel in its 

 centre. 



/. Make a drawing, showing as many of these points as 

 possible. 



II. Examination of the dentary apparatus and its 



