THE PHYLA ARTHROPODA AND ONYCHOPHORA 



closed by the exoskeleton, which is firm in some regions but thinner and more 

 flexible at the joints. Unlike the skeletons of many crustaceans, that of the 

 locust is not hardened by depositions of calcium carbonate; it is composed of 

 scleroproteins and chitin, covered at the surface by a thin waxy layer. As in 

 other arthropods, an approaching molt is preceded by secretion of a new 

 skeleton beneath the old one, through activities of the epidermal cells. 



The head bears a pair of large compound eyes and three small simple eyes, 

 or ocelli (Fig. 15.16). A single pair of antennae is present, bearing a great 

 many sense organs. The antennae may be considered true segmental append- 

 ages that have been modified as sense organs, whereas the eyes and ocelli 

 are primarily sensory structures and not appendages. The so-called "mouth 

 parts" of the locust include segmental appendages as well as structures arising 

 as median, unpaired outgrowths of the head (Fig. 15.17). The true appendages 



Tibia 



Ovipositor 



• Ovipositor 



Meso- Metathorax 



Fig. 15.15. General features of a locust, Melanoplus differentialis . A, female, lateral view; 

 B, female, ventral view. (Redrawn from E. O. Essig, College Entomology, copyright 1942 by 

 the Macmillan Company, printed by permission.) 



445 



