604 EVOLUTION OF ANIMALS Part V 



Abdomen. Each typical segment has a dorsal and a ventral sclcrite, con- 

 nected at the sides by flexible membranes which allow the abdomen free 

 breathing movements (Fig. 30.10). The first pair of abdominal spiracles is on 

 the first segment, one in front of each eardrum; the others are in the same 

 relative positions in the next seven segments. 



In the female grasshopper, the terminal segments form the ovipositor. The 

 ventral sclerite of the eighth segment is prolonged beyond its dorsal mate, and 

 extends between the prongs of the ovipositor and into the genital opening and 

 forms a trough, the egg guide. The most conspicuous parts of the ovipositor are 

 the digging tools called valves. These are closed together like scissors, pushed 

 into the ground and then opened, letting the eggs slip between them through the 



Fig. 30.13. Circulation of blood in the hind wing of the cockroach (PeripJoneta 

 americana). (From Wigglesworth. Courtesy, Ross: Entomology. New York, John 

 Wiley and Sons, 1948.) 



egg guide (Fig. 30.10). The ventral sclerites are lacking on the ninth and tenth 

 segments. The eleventh is represented only by a triangular piece above the 

 anal opening, and a pair of similar pieces, the cerci, one on either side of it. 

 The latter are remnants of abdominal appendages present in the ancestors of 

 grasshoppers when the bodies of insects were longer than now. In the male 

 the sternum of the ninth segment forms a hoodlike cover over the copulatory 

 organs. 



Cuticle and Integument. Neither the outer nor inner surface of the cuticle is 

 smooth. On the outer one there are ridges, spines and hairs. In butterflies and 

 moths, there are numberless scales formed by secretions from cells in the 

 epidermis. Certain cells build up flexible bristles (setae), and after the bristles 

 are formed the cells usually die. On the inner surface of the cuticle there are 

 knobs, hooks and ridges to which the muscles of the body are attached and 

 thus it becomes a supporting framework. 



Color. Insect colors are located in the epidermis, except for a few in the 

 cuticle. They may be chemical colors, due to pigments, or structural ones due 

 to the reflection and interference of fight rays on the surfaces of cells and 



