AN EARTHWORM 63 



prostomium, the median dorsal projection overhanging the mouth, 

 and the indistinct metastomium, which contains the mouth, and 

 is marked off from the prostomium by fine transverse lines. 

 What somites are included in the clitellum ? On the fifteenth 

 somite a pair of prominent transverse slits will be seen. They 

 are the external openings of the vasa deferentia or sperm-ducts. 

 On the fourteenth somite look with the hand lens for the two 

 minute openings of the oviducts. They are difficult or impos- 

 sible to see, except during the reproductive period of the animal. 

 Between the ninth and the tenth and the tenth and the eleventh 

 somites are the two pairs of minute openings of the sperma- 

 thecae, which are also visible only during the pairing season. 

 In each somite, except the first three or four and the last one, 

 is a pair of kidney tubules, called nephridia, which open through 

 the body-wall to the exterior by minute pores on either the 

 ventral or the lateral side near the anterior border of the somite. 

 The ventral integument of a number of somites between the 

 seventh and nineteenth is often swollen by the presence of the 

 so-called capsulogenous glands. Carefully label in your sketch all 

 of these organs which you have observed. 



Exercise 2. Make a similar sketch of the ventral view of the 

 last four somites on a scale of 3. 



Internal anatomy. Pin a large worm, that has been killed, 

 firmly to the wax of the dissecting pan by a strong pin at each 

 end; then make an incision with fine, sharp scissors through 

 the integument in the mid-dorsal line from the forward end of 

 the animal to a point back of the clitellum, taking great care 

 not to cut the viscera lying beneath. It will be noticed that the 

 body-cavity is divided into compartments, corresponding to the 

 somites, by transverse partitions, which are called septa. Hold- 

 ing the cut edge of the body-wall with the forceps, cut the septa 

 where they join it, and then spread out and pin down the body- 

 wall, using many pins on each side. 



