PART. II . 



DETAILS OF THE ANATOMY OF THE FLY 



Section I. The Integument of the Head. 

 PLATE II, FIGS. 1 and 2. 



The head presents several regions which have been variously 

 ivainei by entomologists ; the most important are the occipital or 

 posterior, the frontal or forehead, the cheeks, and the facial, or 

 that between the antennce and the niouth. A correct apprecia- 

 tion of these will materially facilitate the[description of the head, 

 which, with its appendages, consists, as has already been stated, 

 of five segments ; of these however three belong to the 

 proboscis, and three-fourths, that is the ventral and lateral plates 

 of the fifth segment, are incorporated with the thorax ; so that 

 the integument or external skeleton of the head itself consists 

 entirely of the fourth, united with the dorsal plate of the fifth 

 segment. The hard parts of the head are best examined by 

 soaking or boiling it in liquor potassa?, drying it in hot turpentine 

 and mounting it whole in a deep cell in Canada balsam, 

 without pressure: this will also be found the best method of 

 examining most of the integumentary organs of insects with low 

 powers ; it is troublesome at first, but becomes easy by practice 



Some little difficulty may be experienced in realising the 

 relations of the segments of the head, but by considering the 



