10 THE STUDY OF INSECTS. 



first three classes are briefly discussed in this chapter ; the 

 fourth comprises the Insects, and is the subject of the 

 remaining parts of this book. 



FIG. 2. A larva of an insect. 



The following table will enable the student to distin- 

 guish the classes of the Arthropoda.* 



TABLE OF CLASSES OF THE ARTHROPODA. 



A. With two pairs of antennae and at least five pairs of legs. Aquatic 

 animals breathing by gills, p. 11 CRUSTACEA. 



AA. With one pair of antennae or with none. Air-breathing ani- 

 mals. The number of legs varies from six to many. 



*The following is the method of using the analytical tables given in this 

 book: Read carefully the statement of characteristics given opposite A and 

 AA. respectively, and by examining the animal to be classified determine 

 which is true of this animal. This will indicate in which division of the 

 table the name of the group to which the animal belongs is to be looked for. 

 If this division of the table is subdivided, pass to B and BB (also to BBB if 

 it occurs) in this division and determine in a like manner under which the 

 animal belongs. Continue in this way, passing to the letters C, D, E, etc., in 

 regular order till the name of the group is reached. Then turn to the page 

 indicated and read the description or the group given there, comparing the 

 specimens with the description. It should be borne in mind that an analyt- 

 ical table is merely an aid to the determination of groups. As the groups that 

 we recognize are not always sharply limited in nature, we cannot expect to 

 be able in every case to find characters that will serve to distinctly separate 

 them in a table. Therefore when a student has determined by the aid of a 

 key to what group a species seems to belong, he should verify this determi- 

 nation by a study of the characters of that group given in the detailed dis- 

 cussion of it. 



