A CATERPILLAR 21 
short distance to one side of the median line. Turn the integu- 
ment to the right and left and pin it down. If it has not been 
destroyed, observe the heart. It is a straight, transparent tube 
lying in the mid-dorsal line just beneath the integument. Note 
the large, tubular alimentary tract surrounded by delicate, glis- 
tening trachee and by the white and often filamentous fat. Its 
forward portion is the esophagus; the middle and largest portion 
is the stomach-intestine; the narrow portion back of which is the 
intestine ; while the dilated portion which communicates with 
the anus is the rectum. In the forward portion of the body 
cavity, along the wall of the cesophagus, is a pair of delicate 
tubular salivary glands which extend forward and communicate 
with the mouth. Note and trace the course of the much larger 
tubular silk glands on the ventral body-wall; they are also a 
single pair and communicate with an opening in the labium. 
Find and carefully trace the course of the six Malpighian tubes, 
which lie along the stomach and join it at its posterior end. 
Exercise 3. Draw an outline of the opened animal on a scale of 
6, showing the organs above described. Represent the 
segmentation and show accurately the position of the 
organs in their proper segments. 
Sever the cesophagus and remove the stomach and the intes- 
tine from the body. Study the nervous system. Note the 
arrangement of the trachee with reference to the spiracles. 
Note the longitudinal muscle bands which form a part of the 
body-wall; also their segmental arrangement. 
Exercise 4. Draw an outline of the opened body on a scale of 
6, showing and numbering the segments. . Draw in it the 
nervous system, representing accurately the number of 
ganglia, and placing them in the proper segments, together 
with the trachee and muscles. 
The reproductive system consists of two small sexual glands 
and a duct leading from each. There is no external pore. 
