— io — 



therefore often unable to distinguish certain sclerites in one 

 species of insect which we know to exist in another. 

 In such cases the effaced suture is said to be obsolete. 



PARTS OF THE HEAD. 



The principal portion of the chitinized parts of the head 

 are firmly joined together so as to constitute a box which 

 contains what may be called by analog}' the brain of the in- 

 sect and certain other important organs. To this are articu- 

 lated a number of movable appendages. The parts of the 

 head may be classed, therefore, under two divisions ; first, 

 the fixed parts ; second, the movable parts. 



THE FIXED PARTS OF THE HEAD . 



Compound eyes. — The most striking in appearance of 

 the fixed parts of the head are the eyes. These are two 

 large nearly hemispherical objects ; one on each side, form- 

 ing a considerable portion of the latero-dorsal part of the 

 head. 



Study one of the eyes with a compound microscope, using 

 a low power. Note the honey-comb-like structure of the eye. 

 If you have difficulty in seeing this, remove a part of one eye 

 with fine-pointed scissors and mount it on a glass slip. 

 Each of the hexagonal divisions of the eye is a cornea 

 of a distinct eye. These large eyes are therefore compound, 

 and each of the small eyes of which they are composed is 

 termed an ocellus (plural ocelli}. 



Make a drawing showing the honey-comb-like structure 

 of the cornea of a compound eye. 



Note.— The drawings illustrating this course should be made with 

 great care, on good paper. Outline drawings are better than those 

 that are shaded, as shading tends to obscure lines indicating sutures. 

 The drawings should be made first with a pencil, then, after they 

 have been criticized, the lines should be inked. 



Simple eyes. — Cephalad of the dorsal half of each com- 



