50 STUDIES OF ANIMAL TYPES 



viduals or under excitement? Withhold food for half a 

 day from a specimen and then offer it fresh clover or lettuce 

 leaves and note its manner of eating. 



C. EXTERNAL FEATURES. Note that the body is com- 

 posed of three great divisions: head, thorax, and abdomen. 

 Is the abdomen similar in any way to the body of an earth- 

 worm ? Examine the thorax and note that, like the abdo- 

 men, it is divided into segments, but that the division lines 

 are not so plain as on the abdomen. The head is ap- 

 parently not segmented. Actually it is composed of several 

 segments so closely grown together that it is impossible to 

 distinguish them. 



The head end of the body is known as the anterior end, 

 while the opposite end is called the posterior end. When 

 the animal is in its normal position for locomotion on the 

 ground, the side of the body next to the ground is known 

 as the ventral side, while the opposite side, or back, is called 

 the dorsal side. 



Note that the right and left sides of the body of the 

 locust are alike. That is, this animal is bilaterally sym- 

 metrical. This form of structure is characteristic of those 

 animals that move swiftly. 



Head. Note the two large compound eyes. Tear off a 

 piece of the eye and mount on a slide in water beneath a 

 cover glass. Examine with the low-power objective. How 

 does it appear ? 



Make a drawing of twelve of the hexagonal divisions. 

 Each one of these divisions corresponds to a simple eye, 

 and all of them taken together constitute a compound eye. 



Note the round simple eye, or ocellus, in a groove in the 

 middle of the forehead. Note a simple eye at the upper, 

 inside corner of each compound eye. 



