386 



GENERAL BIOLOGY 



Forms breathing 

 free air 



Forms breathing 

 air dissolved 

 in water 



1. Forms running on the surface 

 (water skaters, etc.) 



2. Forms lying on the surface 

 (whirligig beetles, etc.) 



3. Forms hanging at the surface, 

 tipping the surface film (diving 

 beetles, etc.) 



4. Forms far below the surface, con- 

 necting therewith by means of a 

 long respiratory tube. (Ranatra, 

 rat-tailed maggot). 



5. Free swimming forms, (corethra, 

 etc.) 



6. Climbing and clinging forms, 

 (mayfly, nymphs, etc.) 



7. Attached forms, (hydras, bryo- 

 zoans, etc.) 



8. Forms that walk or lie upon the 

 bottom, (crawfish, etc.) 



9. Forms that burrow in the bottom, 

 (Ephemera, etc.) 



Study 48. A laboratory examination of typical pond animals. 



Materials needed: Plenty of living specimens of the 

 several types of pond animals mentioned in the foregoing 

 table ; individual beakers of water in which to examine them. 



First compare together representatives of the two main 

 groups; a whirligig (Gyrinus or Dineutes) , representing the 

 groups that breathe free air, and a Mayfly or damselfly 

 nymph (fig. 225) representing the groups that breathe 

 the dissolved air. Put both in a large beaker of water and 

 watch them ; observe that the beetle carries a bubble of air 

 at its wing-tips as it swims; its respiratory apertures are 

 beneath its wings. Observe the cleavage of the water when 



