CHAP. VII. THE INTERNAL ORGANS OF INSECTS. 43 



itself. In other insects such as the Saw-flies (Fig. 130) it is 

 provided with a piercer or ovipositor (Fig. 129), which is used 

 for the purpose of making punctures in the leaves or twigs of 

 plants, in which to deposit the eggs. The famales of several 

 species of Ichneumon-flies are furnished with an ovipositor, 

 that is frequently as long as the entire body of the insect 

 (Figs. 39, 40, and 131), and composed of several thread-like 

 pieces. 



The males of all insects, having reached the imago state, 

 provide for the continuance of their species, and, being no 

 longer needed in the economy of insect life, soon after die. 



CHAPTER VII. 



THE INTERNAL ORGANS OF INSECTS. 



The nervous system of insects consists essentially of two 

 cords, extending the entire length of the body, and placed 

 nearest to the lower side; these cords are situated one above 

 the other, and the lower cord is enlarged at intervals into 

 knots, called ganglia; from each of these knots a number of 

 cords or filaments extend to the various organs. The fibers 

 which compose these cords, separate at the anterior extremity 

 of the body, so as to pass around the gullet (sesophagus), above 

 which they again unite to form the brain, which is somewhat 

 larger thany of the other ganglia. 



The organs of nutrition consist of an alimentary canal 

 extending the entire length of the insect; it is enlarged in 

 several places, and somewhat resembles the same organ in 

 birds. The gullet (oesophagus) is terminated by a cavity resem- 

 bling the crop in birds; next to this is a smaller muscular 

 organ, analogous to the gizzard; this is followed by a larger 

 and longer cavity, which is the true digestive stomach; this is 

 contracted at the posterior end into the intestinal canal, which 

 is enlarged at the posterior end into what is known as the 

 colon. The liver and the kidneys are not each in compact 



