ANIMALS WITH JOINTED FEET-THE ARTHROPODS 



developed for jumping, whereas the other 

 four are used in walking. The outer wings 

 are leathery and rigid, serving as protective 

 covers for the more membranous under- 

 wings. When the insect is at rest, the under- 

 wings, which are the propelling wings dur- 

 ing flight, are neatly folded under the outer 



225 



bro\n 



fore-qut 



ones. 



The compound eyes of the grasshopper 

 are securely integrated into the head skele- 

 ton, but in other respects resemble those 

 of the crayfish (Fig. 11-20). In addition, 

 three small simple eyes, or ocelli, are lo- 

 cated between the compound eyes. The 

 ocelli function perhaps only in detecting 

 light and dark, which seems unnecessary 

 because the large eyes are so sensitive to 

 varying light intensities. The single pair of 

 antennae vary in length in different species 

 of grasshoppers and function as tactile as 

 well as olfactory organs. Although most of 

 the head is encased in a solid epicranium, 

 the several mouth parts can be traced back 

 to modifications in the crayfish appendage 

 plan. There is a broad upper lip, the la- 

 brum, which is attached beneath the clyp- 

 eus. A pair of lateral, dark colored mandi- 

 bles oppose one another in chewing in such 

 a way as to make it convenient for the 

 animal to bite the edge of a leaf without 

 turning its head. Lying outside the mandi- 

 bles are the maxillae, which are composed 

 of several parts, called palpi ( singular, pal- 

 pus), and used in manipulating the food 

 as it enters the mouth. The lower lip, the 

 labium, possesses two small palpi, resem- 

 bling the larger ones attached to the maxil- 

 lae. Lying in the center of all these parts 

 is the tongue, or hypopharynx. Together, 

 these make an efficient chewing mechanism 

 for handling the kind of food that is eaten 

 by the grasshopper. 



Digestive system. As food is taken in, it 

 is copiously mixed with colorless saliva, 

 secreted by several salivary glands. The 

 food moves through the esophagus to the 

 crop where it is stored, until it passes into 

 and through the gizzard where it is ground 



crop 



caecum 



stomach 



ovary 



excretory 

 tubule 



hind qut. 



heart 



oviduct 



onus 



Sperm receptacle 



Fig. 11-21. Internal anatomy of the grasshopper, dorsaS 



view. 



to a fine consistency (Fig. 11-21). The food 

 then enters the stomach where digestion 

 occurs by the action of enzymes, which are 

 secreted by eight double digestive glands 

 or caeca. Finally the digested food passes 

 into a large and then a small intestine. 

 Small excretory tubules, the Malpighian 

 tubules, empty into the anterior end of the 

 large intestine. The gut opens into the rec- 



