CLASSIFICATION OF INSECTS. 53 



The following table will enable the student to dis- 

 tinguish 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. Page 53 Crustacea. 



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

 The number of legs varies from six to many. 



B. Without antennae and with four pairs of legs, although the maxillary 

 palpi are often leglike in form, making the animal appear to have five 



pairs of legs. Page 55 ArachnidA. 



BB. With antennae. 

 C. With more than three pairs of legs ; and without wings. Page 



57 Myriapoda. 



CC. With only three pairs of legs, and usually with wings in the 

 adult state. Page 58 Hexapoda. 



Class Crustacea (Crus-ta'ce-a). 

 The Crustaceans [Crus-ta'ce-ans). 



The most familiar illustrations of the Crustacea 

 are the crayfishes, the lobsters, the shrimps, and the 



* 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 de- 

 termine 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 of 

 the group given there, comparing the specimens with the description. 

 It should be borne in mind that an analytical table is merely an aid to 

 the determination of groups. As the groups that we recognize are not 

 always sharply limited in nature, we can not 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 



