JULUS, ACRIDIUM 201 



1. The Head.— Is it movable? Does it need to be as mov- 

 able as your own head? It bears several organs. 



(a) The compound eyes. Examine one with a lens or re- 

 move its outer covering and examine it with a compound 

 microscope. You should understand the structure of the 

 whole eye and how it gives a single visual image. 



(6) The ocelli, three in number, one near the middle of 

 the front part of the head and the others placed near the bases 

 of the antennae. 



(c) The antennae. Why are they so flexible? Examine 

 one with a microscope and notice the spines. What are these 



for? 



{d) Mouth parts. These should be studied later. 



2. The Thorax.— Why should it be large and comparatively 

 firm? This portion is more or less distinctly divided into 

 three parts, each of which carries a pair of legs. 



(a) Compare the three legs on one side. Do they have 

 the same number of segments? Do all of the joints of the leg 

 move in the same plane? The five divisions of a leg are, be- 

 ginning with the basal end: coxa, trochanter (immovably 

 joined to the coxa in the leaping legs), femur, tibia, and 

 tarsus, which is composed of four movable pieces. Do the 

 femurs of the leaping legs differ from the femurs of the other 

 legs? Account for this. Determine how the foot is arranged 

 to hold to objects. Have you noticed a grasshopper settle 

 its feet preparatory to jumping? Examine the joint between 

 the femur and tibia. 



(£>) Examine the wings and notice their size, shape, places 

 of attachment, and general character. Do they apparently 

 have different functions to perform? Notice how the posterior 

 wings are folded so that they may be covered by the anterior. 

 Does this seem greatly to reduce their strength? 1 



3. The Abdomen. — Count the number of segments. Each 

 one is covered dorsally by a tergum and ventrally by a 



1 You should examine the posterior wing of a beetle and see how 

 it is folded. 



