A GRASSHOPPER 17 



The male organs. The paired testes which secrete the sperma- 

 tozoa lie above the intestine, bound together by connective 

 tissue and fat. Each testis consists of a bundle of elongated 

 tubes with which a duct called the vas deferens connects poste- 

 riorly. The two vasa deferentia run, one on each side of the 

 intestine, to the ventral side of the animal, where they meet 

 to form a median tube, called the ductus ejaculatorius, which is 

 homologous to the vagina of the female. Connecting with 

 the ductus ejaculatorius are a number of tubular prostate 

 glands which secrete the fluid in which the spermatozoa are 

 suspended. 



Exercise 15. (b) Make a semidiagrammatic drawing representing 

 all the parts of the male reproductive tract. 



The respiratory system. The spiracles have already been noted. 

 They are the external openings of the tracheae, a system of fine 

 air-tubes which extend throughout the entire body of the 

 insect and through which fresh air is introduced into every 

 part of the body. The blood is thus constantly aerated, and 

 there is never any venous blood present. This arrangement 

 results in a very active metabolism, and is one of the causes of 

 the extraordinary amount of energy which characterizes most 

 insects. With the aid of a hand lens examine the tracheae in 

 different parts of the body. They may be easily detected by 

 their silvery gleam. v Notice the arrangement of the main 

 tracheal trunks, including those which connect with the spiracles, 

 also the arrangement of the air-sacs, which are expansions of 

 tracheae. Mount a small portion of the fatty tissue containing 

 tracheae in water or glycerine and examine them with a com- 

 pound microscope. Notice the spiral threads which line the 

 tracheae. 



Exercise 16. Make a drawing of a trachea seen under a high 

 power of the microscope. 



