1 6 PRACTICAL ZOOLOGY 



one hundred and fifty in the grasshopper, perform functions 

 similar to those of the kidneys of other animals. They are 

 known as Malpighian tubes, being named after the Italian 

 naturalist, Malpighi (1628-1694). 



In the preceding paragraphs we have described many of the 

 processes that take place within the body of an insect. This 

 study of function is known as physiology. We have also dis- 

 cussed the organs concerned with these processes; the study of 

 structure constitutes the science of morphology. There are still, 

 however, several systems of organs which perform functions 

 necessary for the insect to cope successfully with its surround- 

 ings. These are concerned with protection (exoskeleton), the 

 reception and transmission of stimuli (sense organs and nervous 

 system), and the continuity of the race (reproductive system). 



Protection. — The outside covering of the grasshopper and 

 other insects, the exoskeleton, is known as the cuticula and con- 

 sists of a substance called chitin. Chitin protects the insect 

 from mechanical injury as well as from contact with water and 

 other liquids. It is formed by the part of the living matter just 

 beneath it. This chitinous covering may be assisted by hairs, 

 scales, and spines which, however, may serve other purposes 

 as well as that of defense. Frequently the exoskeleton is colored 

 in such a way as to conceal the insect amid its surroundings ; this 

 is known as protective coloration. For example, a green katydid 

 is difficult to see when resting on a green leaf. As a further 

 means of protection some insects possess glands which produce 

 evil-smelling or distasteful substances sufficient to prevent at- 

 tacks from dangerous birds and lizards. 



Sensations. — Insects, like human beings, receive impressions 

 from the outside world by means of special structures called 

 sense organs. We may distinguish organs of sight, touch, smell, 

 taste, and hearing. These organs are scattered about on various 

 parts of the body and connected with the central nervous system 

 but the most important ones are borne by the head. 



