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 tracheae and by the white and often filamentous fat. Its 

 forward portion is the oesophagus; 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 oesophagus, 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 oesophagus and remove the stomach and the intes- 

 tine from the body. Study the nervous system. Note the 

 arrangement of the tracheae 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 tracheae and muscles. 

 The reproductive system consists of two small sexual glands 



and a duct leading from each. There is no external pore. 



