AN EARTHWORM 73 
spermatozoa pass in from the spermathece which at once fertilize 
the eggs. The cylindrical membrane then passes completely off 
the worm and its two ends close together. It forms thus a yel- 
lowish, spindle-shaped capsule about as large as a small pea, and 
is called the cocoon. In it the young animals are born. 
Excretory organs. ‘These are the kidneys of the animal. They 
consist of a pair of coiled tubules, called nephridia, which lie 
near the lateral and ventral wall of the body-cavity in each 
somite, except the first three or four and the last one. Each 
nephridium has two openings, a funnel-shaped, ciliated opening 
into the body-cavity, called the nephrostome, and one through the 
body-wall to the outside. The former in each case is attached 
to the anterior side of a septum. The tube passes backwards 
through the septum to the next somite, in which the greater 
portion of it lies, and through the wall of which it communi- 
cates with the outside. The distal, middle, and proximal por- 
tions of the tube differ from one another. The distal portion 
(that next to the nephrostome) is very slender, the middle por- 
tion is much thicker and has glandular walls, and the proximal 
portion is a dilated tube which probably acts as a urinary bladder. 
Notice the four slight projections in the body-cavity on the 
ventral side of each somite. These are the setigerous glands; 
they secrete the sete. 
Exercise 4. Make a sketch of somites 8 to 20, representing dia- 
grammatically the reproductive organs and two or three 
pairs of nephridia lying in their proper somites, and 
label all. 
Crush the sperm-sacs of a fresh worm, that has not been in 
alcohol, mount some of the milky fluid in it, and examine it 
under a compound microscope. Notice the sperm-spheres and 
spermatozoa. 
Exercise 5. Draw a sperm-sphere and a spermatozoan. 
