236 ELEMENTS OF COMPARATIVE ZOOLOGY. 



Study the segments in front of the clitellum, looking for 

 openings of the reproductive organs on the ventral surface. 

 How many pairs of these do you find, and on what seg- 

 ments are they ? Leave a dead worm in water for several 

 hours; can you separate from it an external transparent 

 cuticle ? 



Draw a worm from the side, being careful to get in the 

 right number of segments, back to the posterior end of the 

 clitellum, and bringing out as many of the points dis- 

 covered as possible. 



Pin a worm, which has been in alcohol, with pins pass- 

 ing through the preoral lobe and the hinder end of the 

 body, in a dissecting-pan. With the scissors open the 

 dorsal wall of the body from just behind the clitellum to 

 the anterior end, taking care to cut through only the dor- 

 sal wall. It is best to make this cut just a little to one 

 side of the median line. As you start to lay open the body, 

 notice the partitions (dissepiments) running in from the 

 body-wall and holding the parts together. Do these dis- 

 sepiments correspond in position to the external rings or 

 to the spaces between them ? Do they divide up the body 

 into a series of body-cavities ? Do the cavities of the right 

 side correspond in position with those of the left ? 



Cut the dissepiments with the scissors, and pin out the 

 body -wall. This exposes the digestive tract lying in the 

 axis of the body. In it make out the following regions : 

 (1) A pear-shaped enlargement (pharynx) occupying about 

 half a dozen segments in front. Notice the muscle-fibres 

 going to the pharynx from the body-wall. (2) A narrower 

 tube (oesophagus) leading back through about ten segments 

 from the pharynx, and expanding about segment 16 into 

 (3) a heart-shaped crop, which in turn is followed by (4) a 

 second enlargement (gizzard) of about the same size. (5) 



