FOR WAGGONER’S BIOLOGY 
63 
5. The Excretory System, A pair of excretory organs, “ kid¬ 
neys ” {nephridia), are present in the ventral part of the coelom 
in each segment, except in a few at either end. The kidneys ” 
are very minute. They begin in one segment as funnel-shaped 
structures and continue into the next as looped tubes. In the 
second segment each tube opens to the outside through the ven¬ 
tral body surface. With a lens you may be able to locate these 
structures. 
6. The Nervous System. Beneath the digestive tube on the 
floor of the body cavity lies the white thread-hke nerve cord. An 
enlargement, a ganglion, may be found in each segment. At the 
anterior end, the nerve cord divides and passes around the pharynx, 
forming two gangha on the dorsal side. These ganglia are the so- 
called ‘‘ brain ” of the earthworm. 
7. The Reproductive System. The earthworm is hermaph¬ 
roditic; that is, it has separate male and female sex organs and 
both are present in each individual. The male organs, which can 
be easily located, are three pairs of large white masses at the sides 
of and above the esophagus in segments nine to twelve. The 
female sex organs, the ovaries, are located in the fourteenth seg¬ 
ment and, because of their small size, are more difficult to see. 
The ducts of both the male and female sex organs open to the 
exterior. 
EXERCISE 66 (Supplementary) 
THE CRAYFISH 
I. ,The Living Crayfish. Observe a living crayfish which has 
been placed in an aquarium or pan. By means of what append¬ 
ages and movements does it make its way through the water? 
Place the animal on a table. Repeat your observations. Place 
a ruler or stick near a crayfish. How does it grasp the object? 
Return the crayfish to the water, When it is quiet, drop some 
coloring matter, such as ink, in the water near the place where 
the legs join the body. Note where the colored fluid is drawn m 
and where it is thrown off, The grayfish breathes by means of 
