A CATERPILLAR 15 



Class : Tracheata. Division : Inseda. Order : Lepidoptera 



AN INSECT LARVA: A CATERPILLAR 



Notice that the head, thorax, and abdomen are not set off from 

 one another. The body is thus wormHke in form, there being 

 almost no speciaHzation of the body parts. Determine how much 

 of the body is thorax and how much abdomen. The thorax bears 

 three pairs of jointed legs, each one terminating in a single hook. 

 The abdomen also bears several pairs of legs, which are not like 

 those of the thorax. How many are there and in what do they 

 differ from the thoracic legs ? Find and count the spiracles, which 

 are usually easily seen. 



Exercise 1, Draw an outline representing a side view of the animal 

 on a scale of from 2 to 6 ; number the thoracic and abdominal 

 segments, show the spiracles, and label all the parts. 



Study the head with the aid of a hand lens. Notice the pair 

 of large, convex plates which, with the small, median, triangular 

 plate, form the wall of the head. Near the lower edge of each of 

 the convex plates are several minute ocelli ; count them. On the 

 ventral side of the head find the antennae ; how many joints are 

 there in each ? The mouth parts are between the antennae. The 

 labium is bilobed, and beneath it are the dark-colored mandibles. 

 Just back of these are the maxillae and the labium, the latter being 

 a median, elongated, conical organ between the maxillae. The 

 external opening of the silk glands is in the labium. 



Exercise 2. Draw a front view of the head on a scale of 7. 



Internal Anatomy. With fine scissors make a longitudinal in- 

 cision the length of the animal in the dorsal integument, a short 

 distance to one side of the median line. Turn the integument 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 dehcate, glistening tra- 

 cheae and by the white and often filamentous fat. Its forward 



