150 CIVIC BIOLOGY 



problems, and one which the class can reasonably cover dur- 

 ing the year, and then write the names on slips and let each 

 draw a certain number, or distribute by individual preference, 

 as the class may elect: As these studies progress they should 

 be reported and freely discussed. Thus the biology class may 

 be the organizing center for a better understanding of local 

 insect problems, and enlist cooperation of homes and of boys 

 and girls in the lower grades for more effective effort and 

 better local control. 



The problem of insect classification. It is recognized that for 

 an elementary and practical course the complete classification 

 of insects is too difficult and would take too much time.. The 

 vast number of species, more than three hundred thousand, are 

 commonly grouped into nineteen orders, and any student who is 

 specially interested can find the subject fully treated in manuals. 

 For all elementary purposes it will be sufficient to learn the 

 names and characters of the seven more important orders. Every 

 one ought to know what we mean by a "fly," a "bee," a "bug," 

 a " moth or butterfly," a "locust," a " beetle," a " lacewing." 



Since classification consists in gathering into groups forms 

 with similar structures and parts, we need to learn something 

 of the way an insect is constructed. . To begin, take any large 

 insect, a beetle or grasshopper, and work out all the apparent 

 subdivisions of the body. Note the three main subdivisions 

 head, thorax, and abdomen and locate the breathing pores 

 (spiracles) as indicated in Fig. 77. Insects, spiders, and myria- 

 pods, instead of having one pair of nostrils, a windpipe, and 

 lungs to which the blood is brought to be oxygenated, circu- 

 late the air directly to the tissues by means of fine, elastic, 

 branching tubes. These are known as tracheae, and these ani- 

 mals are known, since this is a character of great significance, 

 as tracheates. Contact insecticides oil films on water for mos- 

 quitoes, oil-emulsion or soapy sprays depend upon clogging 

 these fine breathing pores and thus smothering the insect. 



