62 INSECTS. 



life, and are especially worthy to be studied alive. Study 

 them so, either at home or in their native pools. 



Study of a Live Specimen. Observe : 



1. The boat-shaped body. 



2. The oarlike position and action of the long hind legs. 



3. The winy tips reaching the surface, and admitting 

 beneath the wings a supply of air, which may be breathed 

 when the insect is at the bottom. 



4. The thin layer of air surrounding the thorax (easily 

 seen at the joints when the body is bended). 



Place one on a dry surface : see it walk. 



Throw an adult up into the air : see it fly. It can 

 arise in flight direct from the water. 



Study the external features in order, as outlined for 

 other insects, noting especially : 



1. The junction of the head with the prothorax. 



2. The position of the antennce. 



3. The shape, size, and position of the eyes. 



4. The absence of ocelli. 



5. The sharp, lateral edges of thorax and abdomen. 



6. The hairiness of parts. 



7. The form, size, and position of the legs. 



8. The structure of the tarsi (use a lens). 



9. The structure and position of the wings. 



10. The relation between the spiracles and the air 

 inclosed beneath the wings. 



Then answer these questions : 



1. What advantages are secured to the back-swimmer 

 by the peculiar shape of its body? 



2. Need locomotive organs be more complex for pro- 

 gression in the water, or on the land? Why? 



3. What other devices for aquatic respiration have 

 you studied, and what points had each in common with 

 the respiratory method of this insect? 



