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PART II. 



As it is my desire to make this report a "Manual of Economic Ento- 

 mology for Elinois" and through it to familiarize the farmers and hor- 

 ticulturalists of our State, as far as possible, with insects which 

 destroy their crops, injure their fruit and ornamental trees, and infest 

 their gardens, it is proper that I should first explain the terms used 

 and give in as plain and simple language as possible the character of 

 the insect class and of its larger sub-divisions. I am fully aware that 

 in doing this I shall have to go over ground that has been repeatedly 

 traversed, therefore I shall be brief, avoiding as far as possible repeat- 

 ing what has been so well presented by Dr. LeBaron in his Fourth 

 Report, giving only such explanations as will suffice to render intel- 

 ligible to the general reader what is herein written, and what may 

 be necessary for practical purposes. • 



Those who desire further information on this subject are referred to 

 more extensive entomological works. 



'What is an Insect f This is the first question presented when we 

 attempt to study entomology, or that science which treats of insects, 

 and it is necessary that we should be able to answer it whether we 

 investigate them scientifically or for practical purposes only. 



If the reader will examine carefully a common wasp he will notice 

 that the boch' is divided by transverse indentations into three re- 

 gions ; the front part being the head, which bears one pair of jointed 

 tl i read-like horns called antennse ; the middle portion which is called 

 the trunk, or more correctly the thorax, has attached to it on the under 

 side six articulated legs, on the upper side two pairs of wings ; the 

 hinder part, which is composed of similar rings, is the abdomen. 



If we examine a common cray-fish, we shall find the head consoli- 

 dated with the thorax, so as to leave no line of distinction between 

 the two ; it also has ten legs and two pairs of antennae. If we now 

 take a spider or tick [we do not find the body divided into three parts, 

 two of them and sometimes all three being apparently consolidated 

 into one ; we shall also find eight legs and no antenna?, though in 

 some we may observe a j)*r of feelers which look very much like a 

 fifth pair of legs. 



An examination of a milliped or "thousand legged worm," shows a 

 distinct head which bears one pair only of attennse, but the rest of 

 the body consists of numerous similar rings, presenting no distinct 

 thorax, and the legs are numerous. 

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