114 MANUAL OF ANIMAL BIOLOGY 



I. THE GRASSHOPPER 



A. External Structure 



The body of the Grasshopper, in common with that of all 

 Arthropods, is enclosed in a resistant chitinous exoskeletal covering, 

 the cuticula, which is formed as a secretion of the underlying epi- 

 thelial cells. The division of the body into three basic regions, 

 head, thorax, and abdomen, is clearly indicated. The body of the 

 Grasshopper consists of twenty segments, of which six constitute 

 the head, three the thorax, and eleven the abdomen. As previ- 

 ously noted in the Crayfish, the segmentation of the exoskeleton of 

 the head and thorax is not well-marked. We may now consider 

 the external structural features of these three primary body 

 divisions. (W. f. 54.) 



1. Head 



The portion of the exoskeleton enclosing the head is termed the 

 epicranium. Viewed from the anterior, or facial, aspect the 

 following arrangement of parts may be noted : 



(a) A pair of large compound eyes which protrude from either 

 side of the head. Each of these, as in the Crayfish, is composed 

 of a great number of independent visual units, the ommatidia. 

 Three simple eyes, or ocelli, 1 are present on the front of the head : 

 one near each compound eye and one in the midline between the 

 attachments of the antennae. 



(6) A pair of relatively short, jointed antennae which are 

 attached to the front of the epicranium near the compound eyes, 

 and project anteriorly and dorsally. 



(c) Ventral to the antennae a definite line marks the ventral 

 edge of the epicranium, and below this a portion of the exoskeleton, 

 known as the clypeus, is found. A broad upper lip, or labrum, 

 lies ventral to the clypeus. 



(d) Removal of the clypeus and labrum reveals : (i) a pair of 

 serrated jaws, or mandibles, for grinding ; (ii) a pair of maxillae, 

 each of which bears a segmented maxillary palp ; and (iii) a 

 lower lip, or labium, which is divided in the median line and bears 

 a labial palp on each side. The mouth, with (iv) a tongue-like 

 hypopharynx, opens back of the mandibles. 



The mouth parts of the Insects as a group show a remarkable 

 range of variations in correspondence with the various feeding 



1 Singular, ocellus. 



