12 



FOREST ENTOMOLOGY. 



femur; then we have a long joint called the tibia; and finally, the 

 joint called the tarsus, which is known as the foot. Fig. 13 is a 

 representation of the different parts of the leg. 



The foregoing characters represent the more important points as 

 regards external structure, but it is somewhat more difficult to deal 

 with internal structure and function. To deal with too many details 

 would simply embarrass the ordinary student, and at the same time 

 the subject cannot possibly be intelligible to the student if too few 

 points are presented. 



The accompanying diagram (fig. 14), representing a longitudinal 



Fig. 14. Diagram of longitudinal section of an insect, showing principal anatomical points of an 

 insect. (From 'Text-Book of Zoology,' by Dr J. E. V. Boas.) 



1-3, first and third pairs of legs cut away; a, anus; c, cerebral ganglion; ch, mesenteron ; 

 e, proctodeum ; g, genital aperture ; h, heart ; k, crop ; in, mouth ; n, ventral ganglion ; 

 sp, salivary gland ; u, malpighian tubule ; ft', ovary. 



section of an insect, shows the relative position of the more important 

 anatomical points from a side view. 



jfcThe nervous system of an insect resembles that of most other 

 animals, inasmuch as the terminal seat of the nerve-centres is the 

 brain, whence proceed other nerve-centres and nerves all over the 



body. The nerves receive impres- 

 sions from the outside world, which 

 react on the organism, and thus stim- 

 ulate or restrain muscular action. 

 Fig. 15 shows a photograph of a 

 horizontal section through the head 

 of a honey-bee. 



The various convolutions of the 

 brain should be noted ; and as the 

 development of these convolutions is indicative of intelligence, it is 

 no wonder that the bee, in this respect, is considered as approaching 

 nearer to man than any other animal. 



The respiratory organs of an insect are composed of a system of 



Fig. 15. Horizontal section through the head 

 of a worker bee, showing eyes and brain. 

 (Section and photo by A. Flatters.) 



