THE INTERNAL ANATOMY OF THE LOCUST 293 



spiracles. Soon after entering the body the tracheae unite to form 

 two large lateral trunks. From these, dorsal branches are given off, 

 which unite, forming two parallel dorsal trunks. Running off from 

 both the dorsal and lateral trunks are smaller branches, which 

 separate into extremely minute tubes and ramify through all the 

 tissues. 



Exercise 37. If fresh specimens are at hand, mount in water some of the 

 fatty tissue surrounding the alimentary tract, and examine under the compound 

 microscope. The tracheae will be seen as much-branched silver-colored tubes. 

 Make a careful drawing. 



Exercise 38. Make a drawing of the side view of the locust, with the alimen- 

 tary tract and reproductive organs removed, showing the general arrangement 

 of the muscular, tracheal, and nervous systems. 



7. Circulatory system. The circulatory system consists of a 

 dorsal, median, tubular heart. This can be seen in fresh specimens 

 by removing the dorsal body wall. 



Exercise 39. In order to observe the rhythmic contraction of the heart, 

 obtain living larvae of mosquitoes, dragon-flies, or May-flies. Place them in 

 water on a slide and examine under the microscope. Draw. 



