PHYLUfA ARTHROPODA 



309 



Figure 16.19. Wings of the cockroach, showing the numerous veins characteristic 

 of the more primitive insects. 



tarsal joints allow freedom between the position at which a grip is best 

 maintained and the direction of the tibia. 



The anterior wings (Fig. 16.19) at rest are folded over the body, 

 covering the posterior wings. They are slender and leathery, protecting 

 the hind wings when the animal passes beneath objects. The posterior 

 wings are pleated, and fold fanwise when not in use. In flight all four 

 wings are held out to the sides and flapped dorso-ventrally. Cockroaches 

 seldom fly, and do so primarily in search of new habitats. Each wing is 

 strengthened by a number of hollow veins which are continuous with 

 the hemocoel of the body. Their arrangement or venation is a prom- 

 inent characteristic in insect classification. 



The abdomen (Fig. 16.17) is made of ten segments, each slightly 

 overlapping the segment behind and divisible into a dorsal notum and 

 ventral sternum. Nota of the eighth and ninth segments are telescoped 

 completely out of sight beneath that of the seventh, and the tenth ex- 

 tends posteriorly as a notched plate. From the sides of the tenth seg- 

 ment emerge a pair of cerci, antenna-like structures sensitive to air 

 currents and low frequency sounds. The anus opens posteriorly on the 

 tenth segment, with the reproductive openings beneath it. 



Between the prothorax and eighth abdominal segments are ten pairs 

 of spiracles, openings to the respiratory system, between adjacent seg- 

 ments just beneath the nota. 



1 42. Internal Anatomy of the Cockroach 



The digestive tract (Fig. 16.20) includes fore-, mid- and hindguts as in 

 the Crustacea. The mouth opens into a mouth cavity that receives ducts 

 from a pair of large, bilobed salivary glands in the mesothorax. Their 

 secretion digests starches. The mouth cavity continues as a long narrow 

 esophagus to a posterior enlargement, the crop. The crop opens into a 

 small muscular gizzard containing six strong teeth and numerous bris- 

 tles. All of these organs are part of the foregut and are lined with 

 chitin. 



The gizzard opens into the midgut, a narrow stomach. Anteriorly 



