162 



LOCUSTS, BUTTERFLIES, BEES, WASPS 



nately contracting and expanding movement of the abdo- 

 men called the respiratory movement." 



The circulatory system of the locust. — The blood vessels 

 and the circulation of the blood in insects are well shown 

 by a study of the locust. The circulation of insects is not 

 well developed. The only blood vessel in the locust, for 

 example, is a long, slender, tubular organ that runs along 

 the dorsal side of the body cavity in the abdomen and 

 thorax and extends into the head. This is known as the 

 dorsal vessel, and that part of it lying in the abdomen is the 

 heart, while the anterior part, in the thorax, is the aorta. 



The heart is closed at its posterior 

 end, but has openings along each 

 side through which the blood enters 

 and, by contractions of the heart, 

 is forced forward through the aorta 

 into the head. Valves within the 

 heart prevent the blood from flow- 

 nervecoTYt ing backward through it. The 



Brain gangUa 



'Thoracic 

 gancfUa 



iAbdominal 



ganglia 



blood is usually a colorless liquid 

 and fills all the spaces of the body 

 cavity, literally bathing the tissues 

 and organs of the insect. It does 

 not carry oxygen because this is 

 done by the air tubes. Its func- 

 tion is to carry the products of di- 

 gestion from the alimentary canal. 

 The nervous system. — The brain 

 consists of three large ganglia 

 closely connected and lying above the gullet in the head. 

 From the brain the nerve cord passes posteriorly, one 

 strand going down the left side of the gullet and the other 



Fig. 101. — Nervous system 

 of a grasshopper. 



