14 PRELIMINARY EXERCISES 



abdomen. Therefore, all insects fall into one great group 

 known as a class (Hexapoda, or Insecta). To go further 

 and compare insects with crayfish, lobsters, spiders, sow 

 bugs, etc., we should find that all of these animals have 

 segmented legs and segmented bodies. Therefore, on account 

 of these similarities, they are all assembled in one great 

 group known as a branch ( Arthropoda) . 



If time is available, no better scheme of improving it 

 could be devised than by devoting a few exercises to the 

 classifying of a few common insects. For example, collect 

 several specimens of our common insects representing the 

 orders of locusts, bugs, flies, beetles, bees, and butterflies. 

 Make a careful study of the leading characteristics the 

 similarities and differences of the individuals until the 

 insects of like characteristics can be grouped by themselves. 

 Name the groups (orders). Select some cabbage butter- 

 flies and some swallow-tail butterflies. Note the differ- 

 ences and similarities and separate them into groups con- 

 taining like individuals/ Name the groups (genera). 

 Finally, select some individual swallow-tail butterflies and 

 separate them into species. 



IV. PLANT CELLS 



Materials. Pond scums, glass jars, melon vine, moss, glass 

 slides, cover glasses, compound microscope. 



Directions. Collect some pond scums from different 

 sources and keep them in glass jars, changing the water 

 now and then to prevent it from becoming too stagnant. 

 Spirogyra is a very common species of pond scum. It 

 may be recognized from the green, spiral bands inside the 

 long, slender threads. 



