230 



COLLEGE ZOOLOGY 



Other 

 Arthropoda 



Figure 130. There are about 875,000 known living species of arthropods in the world. Of 

 these approximately 850,000 species are insects, and 25,000 species are other arthropods. Insects 

 comprise about 97 per cent of the species of known arthropods. 



forewings, enlarged hindlimbs, auditor}' or- 

 gans, and structures for making sounds. It 

 is of considerable economic importance. 



THE GRASSHOPPER 



External anatomy 



Like the crayfish, the grasshopper is cov- 

 ered by an exoskeleton (Fig. 131) which 

 protects the delicate systems of organs 

 within. This exoskeleton is the cuticle, 

 which contains chitin and is divided into 

 a linear row of segments. As in the crayfish, 

 the cuticle is soft in certain regions, thus al- 

 lowing movements of such structures as the 

 abdomen, wings, legs, and antennae. These 

 softer regions are known as sutures. The 

 body wall consists of the cuticle beneath 

 which is a layer of cells, the epidermis, 

 which secretes it, and under this is a base- 

 ment membrane. Each segment is made up 

 of separate plates (pieces), which are known 

 as sclerites; usually some of the sclerites of a 

 typical segment cannot be distinguished 

 because the sutures are indistinct or absent. 



In the grasshopper the body is divided into 

 three groups of segments that constitute the 

 head, thorax, and abdomen. 



Head 



The head is composed of fused segments 

 (Fig. 132). These are not visible in the 

 adult, but may be observed in the embryo, 

 and are indicated by the paired appendages 

 of the adult. The dorsal region of the head is 

 known as the vertex; the front portion is 

 called the frons; and the sides are the 

 cheeks or genae. The rectangular sclerite be- 

 low the frons is the clypeus. On either side 

 of the head is a compound eye, and on top 

 of the head and near the inner edge of each 

 compound eye is a simple eye (ocellus). 



Mouth parts 



The food of the grasshopper consists of 

 vegetation which it bites off and grinds up 

 by means of its chewing mouth parts (Fig. 

 132). There is a labrum or upper lip at- 

 tached to the ventral edge of the clypeus. 

 Beneath this is the membranous tonguelike 

 organ, the hypopharynx. On either side is a 

 hard jaw or mandible, with a toothed sur- 



