40 INVERTEBRATE ZOOLOGY 
just ventral to the stomach, taking care not to injure the brain, 
which lies in front of the stomach, or the two slender nerve- 
connectives, which lie on either side of the esophagus. Sever * 
the rectum near the anus. Remove the entire digestive tract 
from the body and place it in a pan of clean water. The liver 
is so soft that it may not be possible to remove it entire. 
Notice the boundary between the intestine and the somewhat 
larger rectum. In the crayfish the rectum is much longer than 
the intestine; in the lobster the opposite is true. In the lob 
ster notice the blind-gut or appendix which joins the rectum near 
its anterior end. 
Exercise 23. Make a diagrammatic sketch of the digestive tract. 
Cut open the stomach by a ventral incision and wash it out. 
Observe its chitinous lining and the dark brown chitinous teeth. 
This chitinous lining is a continuation of the cuticula which 
covers the external surface of the body and is moulted with 
the cuticula. During certain parts of the year a pair of large 
calcareous bodies called gastroliths are imbedded in the lining of 
the stomach. They remain in the stomach after the moulting 
of the cuticula and furnish lime for the new cuticula, which at 
onte grows rapidly. 
Exercise 24. Make a sketch of the inner surface of the stomach 
showing the teeth. 
The excretory system. Notice in the extreme forward end of 
the body-cavity, just in front of and below the stomach, a pair 
of pale greenish bodies. These are the kidneys or green glands. 
Each one is made up of two portions, the smaller glandular por- 
tion, next to the body-wall, and the larger saccular portion, or 
urinary bladder, next the stomach. From the latter the ureter 
leads to the external openings which have already been noted. 
Exercise 25. Draw a view of the forward end of the body- 
cavity showing the kidneys as they lie in position. 
