POND LIFE. I 13 



the chief part of the head ; the antennas — these are 

 unusually short and thick (Fig. 91 represents one of 

 the antennge of a whirligig-beetle greatl)' 

 enlarged); the compound eyes — these are 

 quite prominent, and are situated a consider- 

 able distance from the margin of the head. 



4. Study the head as seen from below. Here 

 a very remarkable thing will be seen— namely, a 

 pair of large compound eyes in addition to the pair 

 already observed on the upper side of the head. It 

 should be said, however, that these insects really 

 have only two compound eyes, like other insects ; but 

 each eye is divided within the head, one part extend- 

 ing to the upper surface of the head and the other to 

 the lower surface. What peculiarity in the mode of 

 life of the whirligig-beetles renders this arrangement 

 of eyes desirable ? 



5. Study the mouth-parts and observe that in- 

 stead of a beak for sucking, as with the water-strid- 

 ers, these insects have jaws fitted for biting. 



6. Make a drawing of one of the front legs, and 

 label the following parts : coxa, trochanter, femur, 

 tibia, tarsus, claws. 



7. The sexes of whirligig-beetles can be distin- 

 guished by the fact that in the males the segments of 

 the tarsus of the fore legs are flattened and furnished 

 with a spongy cushion of hairs beneath, while in 

 the females the segments are more nearly cylindrical 

 and do not bear cushions. Separate the sexes of 

 these insects in your collection. 



8. Study the middle and hind legs and observe 

 their strangely modified form. While the fore legs 

 are oarlike in form, these are modified into short and 



