242 MANUAL OF ZOOLOGY SECT. 



consists of three segments, which are usually firmly united 

 together. The abdomen contains from ten to eleven seg- 

 ments. 



The appendages are also very constant in their arrange- 

 ment throughout the Insecta, though variously modified in 



form in the different orders, 

 in accordance with differ- 

 ences in mode of life. The 

 head (Fig. 141) bears a 

 pair of antennae, a pair of 

 mandibles, and two pairs 

 of maxillae. The antennae 

 vary a good deal in size 

 and shape in different 

 insects. The mandibles 

 (Fig. 142, md) lie at the 



FIG. 141. Periplanetaamericana. Lateral c\A e ^ n f the month in 



view of the head and its appendages. S .Ul, ] 



cerv, one of the cervical sclerites; ey f ront Q f w hich is a ITlOVa- 

 eye; V?,gena; man, mandible; max 1 , 



first pair of maxillae; max*, second pair ^\Q labnim Or Upper lip 

 of maxillae (labium). 



(Ibr). Each mandible is 



a single solid piece, and is devoid of palp. The second pair 

 of maxillae (mx. 2) are united in their basal portions to form 

 a lower lip (labium). Jointed palpi (pnt) are borne both 

 by the first pair of maxillae (maxillary palpi) and by the 

 second (labial palpi). All the jaws become differently 

 modified in the different orders in accordance with differ- 

 ences in the nature of the food. Insects, which like cock- 

 roaches and beetles, masticate hard substances, have the 

 mandibles strong and sharp and the maxillae well developed, 

 and adapted to act as masticatory organs. Insects which, 

 like cicadas, bugs, lice, and plant-lice, live on the juices of 

 plants or animals, have the jaws in the form of sharp stylets, 

 enclosed in a sheath or proboscis, for piercing the integu- 



