264 ELEMENTARY ZOOLOGY. 



There is good field for studies, on the part of the students, 

 of special adaptations in insects to special modes of life. 

 There is no other group of animals so favorable for this 

 kind of investigation. For example, we may take an 

 illustration in the form of the body itself. In the cock- 

 roach, which is kin to the grasshoppers, the body is very 

 much flattened dorso-ventrally. This is interpreted 

 as an adaptation to the habit of crawling and living in 

 concealment under objects. In the case of the fleas, the 

 flattening is right-left. This enables them to crawl 

 with less difficulty among the hairs of the hosts upon 

 which they live. 



274. Relations of the Arthropods to Man. Few of 

 them are of direct use to man as food. The lobsters, 

 crabs, shrimps, crayfish among the Crustacea; and the 

 honey of the bee, among the insects, about complete the 

 list. Locusts are said to have been eaten in cases of 

 extremity, where they have devastated the land. 



The silk of the silk moth is important as a source of 

 supply of a most beautiful cloth, and the web of spiders 

 has been used in the same way, but not on a commercial 

 scale. 



Many of the plants useful to man are pollinated by 

 insects. This is true of red clover, w r hich is pollinated 

 by the bumble bees, and of many of our fruits. But for 

 a small fly, the formation of fruit by fig trees is impossible. 

 This insect was not native to America and had to be 

 imported before any success was possible in the fig culture 

 of California. 



In the adult stage they may destroy crops, spread 

 contagious diseases, devour stored grain, and become 

 a menace to man and the domestic animals. In the 



