GENERAL CONSIDERATIONS ABOUT INSECTS. 59 



66. Tell of the nest habits of mud wasps. 



67. Discuss the intelligence of ants. 



General. 



68. Tell how an insect breathes. 



69. What is meant by homologous parts? 



70. What are vestigial organs? 



71. What is protective coloration? 



72. What is mimicry? Give examples. 



73. How does the resemblance to Anosia protect 



Basilarchia? 



74. Of what is the skeleton of an insect composed? 



How is it joined together? 



75. Describe the nervous system. 



76. What senses and sense organs have insects? 



Some General Considerations About Insects. 



There are about 250,000 species of insects already 

 known and described, and these are perhaps not more 

 than one-tenth of the species that exist. With the 

 probable exception of some classes of Protozoa, the 

 insects constitute the largest class of animals, both in 

 individuals and in species. Some insects are useful 

 to man. Shellac, cochineal, gall nuts, silk, beeswax, 

 and honey, are produced by them. The greatest 

 benefit, however, is derived from their assistance in 

 fertilizing plants. 



Insects do much injury to mankind. Besides the 

 personal discomforts arising from such insects as flies, 

 mosquitoes, etc., the injury that insects do to crops in 

 the United States each year is very great. Mr. Riley 

 once estimated it at $300,000,000 per year. 



The study of insects is called Entomology. In 

 studying insects, it is quite helpful to collect and pre- 

 serve them. An insect net is useful for collecting 

 many kinds of insects. The net should be about 



