THE COMMON KED-LEGGED LOCUST 7 



pass through and mingle with the blood in the general body- 

 cavity. This process is called absorption. The anterior part 

 of the intestine is thin-walled, and absorption may take place 

 there and also in the caeca. The unused food-material is 

 removed from the body by means of the anal opening. 



The Circulatory System. When the food has been acted 

 upon by the various digestive fluids, and so changed that it 

 may be used to supply the different organs with nourishment, 

 it is distributed over the body by the circulatory system. At 

 the same time certain waste matters are taken away and carried 

 to organs the function of which is to remove them from the 

 body. In the case of man and many other animals, the circu- 

 latory system is also the means by which oxygen is carried to 

 all the organs ; but, as we shall see in a moment, this work is 

 otherwise provided for in the locust. As soon as the prepared 

 food has been absorbed by the walls of the stomach and intes- 

 tine it mingles with the blood, which flows through the body- 

 cavity in sinuses (spaces between the various organs), though 

 not in definite blood-vessels. The blood is propelled by a 

 tubular, pulsating vessel, or heart (Fig. 3, 21), which extends 

 through the abdomen just beneath the dorsal surface. On 

 account of its position in the body it is often spoken of as 

 the dorsal vessel. The heart is prolonged anteriorly into a 

 tube leading to the head, and is partially divided by valves 

 into eight chambers, which permit the movement of the blood 

 only from the posterior to the anterior end. When the blood 

 has been passed out into the general body-cavity it returns 

 through a closed tube (ventral sinus) between the muscle 

 masses lying in the lower (ventral) part of the body, and 

 reenters the heart through side openings. 



The Respiratory System. The function of the respiratory 

 system is to provide for a constant supply of oxygen for all 

 the organs of the body. This is accomplished by a system of 

 tubes, called tracheae, communicating with the surface by the 



