8 AN IXTRODl'CTIOX 7\< 



The sclerites constitute the greater part of the l>uly-\vull. tin 

 membranous portio: itiii^ them being in m< 



Usually tlu A' portions are mere 



lines ; they .ire then called .\v?////. 



:tly the .sutures becom, 

 tirely effaced. We are therefore often 

 unable to distinguish certain 

 in one species of insect which we k 



\ist in another. In such ca>rs the 

 effaced sutures are said to be obsoi 

 :i*iiicosa. The segments of the body in a fully 



developed insect are grouped into three regions: head, t/wrti.v. .uul 

 abdomen (Fig. 15). In the larval state this grouping of the sc-ments 

 lot well shown. 



The Head. 



The head is the first of the three regions of the body. It is sup- 

 posed to be formed of several body-segments grown together; but 

 entomologists differ in their views as to the number of Moments 

 that have entered into its composition. 



It does not fall within the scope of this work to enter into this disci; 

 I The main point, however, can be stated here. A careful study of tlu- \arious 

 forms of Arthropods shows that the typical body-segment possesses a pair of 

 legs, and only one pair. It is known that certain mouth parts (mandibles. 

 maxillae, and labium) are modified legs. (This fact is easily seen in many 

 Crustacea.) The antennas and the eyes may also be modified legs.* It follows 

 that if we find represented in the appendages of the bead tlu- apprmhu 

 several segments, the head itself must consist of several segments coal< -. <-d. 



The principal portion of the chitinized parts of the head an firm- 

 ly joined together so as to constitute a box which contains the biain 

 of the insect and certain other important organs. To this are artic- 

 ulated a number of jointed appendages. The parts of the In .id 

 may be classed, therefore, under two divisions : first, the fixed parts; 



>nd, the movable parts. 



The Fixed Parts of the Head. 



In addition to the external portions of the organs of vision (the 

 Compound eyes, and the simple eyesi, the fixed p;rts of the head 

 consist of four . Three of these sclerites (occipu: 



*The belief that the eyes are modified legs is based on the fact that in <rrtain Crusta- 

 cea the eyes are situated on stalks which are jointed appendages of the h 



