312 THE ANIMAL KINGDOM 



^o win^S 



Spiracles 



TracheoleS 



B 



Tra.ch.ea.' 



Epiderinis 



Spirally 

 thickeried chitin' 



Figure 16.22. Tracheal system of the cockroach. A, The major tracheal trunks. 

 (After Parker and Haswell.) B, Diagrammatic view of the tracheoles of a single cell. 

 C, Detailed structure of a trachea. {B and C adapted from Wigglesworth.) 



The hemocoel of insects is a single, large, branched space without 

 a separate pericardial sinus. In the cockroach the heart is a long dorsal 

 tube, expanded in each segment of the thorax and abdomen. In each 

 segment a pair of valves admits blood from the hemocoel. Anteriorly 

 the heart continues as a short artery that ends behind the brain. Con- 

 traction usually proceeds forward along the heart and can be seen 

 through the body wall of an uninjured roach. Relieved of respiratory 

 duties by the tracheal system, the blood in labiates serves primarily to 

 distribute nutrients to the body and to transport wastes to the Mal- 

 pighian tubules. 



The male cockroach has a terminal complex of copulatory organs 

 (Fig. 16.20) formed from the sternum of the last segment and the much 

 modified appendages of the eighth and ninth abdominal segments. Ex- 

 cept for a pair of ventral styles on the ninth segment these organs are 

 usually retracted into the body. Small testes lie dorsally in the fourth 

 and fifth abdominal segments from which a pair of sperm ducts lead to 

 seminal vesicles, clusters of delicate tubules in the sixth and seventh 

 segments where the sperm are stored. At copulation sperm are passed 

 through a single stout ejaculatory duct that opens among the copulatory 

 organs. 



The female has a pair of large ovaries, each composed of eight lobes 

 in segments 4 to 6. Within each lobe the smallest eggs are anterior, the 

 larger and more mature eggs posterior, giving it a beaded appearance. 

 Paired oviducts from the ovaries join to open ventrally on the eighth 

 segment. The ninth segment has a ventral opening to a seminal re- 



