AN EARTHWORM 69 
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- 
thece, 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. 
