272 



METAZOAN PHYLA 



many segments but vary greatly in their length and still more in the 

 details of form and structure. They bear a variety of sense organs which 



Anfenna 



Profhorax 



Wings 



L a brum 



Mandible 



Moixilla 



Femur Sp/rac/es 



Labiuni 



Tibial 



Tarsus 



Fig. 170. — Diagram of a locust with parts of the body separated to show metameres and 

 other structures. Abdominal metameres numbered in reman numerals. {Modified from 

 several previous authors.) 



are tactile, olfactory, or auditory in function. The difference in structure 

 of those of the male and female frequently serves to distinguish the sexes. 



The mouth parts of insects are 

 of two distinctly different types, 

 one fitted for biting, the other for 

 sucking. The former are referred 

 to as mandibulate, the latter as 

 suctorial. Mandibulate insects 

 (Fig. 171) possess an upper lip, or 

 labrum, and a lower lip, or labium. 

 Between these and meeting in the 

 median line are two strong jaws, 

 or mandibles, and behind the 

 mandibles is a pair of maxillae. 

 Both the maxillae and the labium 

 bear jointed organs known as 

 palpi. The mandibles are used 

 for chewing and work transversely, 

 the labrum and labium preventing 

 the escape of the food from 

 between them. The maxillae help 

 to feed the food into the man- 

 dibles, while the palpi are sensory, sending impulses into the nerv- 

 ous system which determine the activity of the other mouth 



Compound eye 



Anfenna 



Clypeus 



Mandible 



Labrum 



Moxilla 

 Labium 

 Maxillary 

 palpus 



Labial palpus 



Fig. 171. — Front view of the head of 

 a lubber grasshopper, Brachystola magna 

 Girard, from Nebraska. X 3}-^. Illustrates 

 biting mouth parts. 



