THE HEAD. 55 



69. 



Before we pass on to our general consideration of the organs [of the 

 suctorial mouth, we must give the most remarkable differences of the 

 above-named masticating organs; but we will first notice the relations 

 of the head to the thorax, as well as the proportions of its own parts. 



We observe in the head the direction in which its longitudinal 

 diameter stands to the axis of the body. If they form one plane, 

 it is called PROMINENT (promincns, Elater) ; PORRECT when it pro- 

 jects, likewise horizontally, far from the thorax (Agra) ; NUTANT 

 (nutans*) when its longitudinal diameter forms an obtuse angle with 

 the axis of the body (Feronia, Amara, Harpalus ; PERPENDICULAR 

 (perpendicukire) is when its longitudinal diameter forms a right angle 

 with the axis of the body (Saperda, Diptera, Hymenoptera'}. 



We must next observe the manner of its connection with the thorax. 

 FREE (exsertum or liberuni) is a distinctly visible head, never 

 covered by the thorax (Agra, Anthia, Hymenoptera , Diptera). 



INSERTED (insertum), when it is partly, particularly the occiput, 

 concealed within the thorax. 



RETRACTED (retractuin), when it is concealed as far as the brow 

 within the thorax (Bupreslis). 



CONCEALED (abscondituni), when it is entirely withdrawn within 

 the thorax, or is covered above by the thoracic plate (Cassida). 



RETRACTILE (retractile) when a thus concealed head can be pushed 

 forwards at the will of the insect (Hi&ter). 



VERSATILE (versatile), when it can be freely moved every way 

 (Hymenoptera, Diptera). 



From its anterior margin it is distinguished into CLYPEATE HEAD 

 (c. clypeatum, PI. IV. f. 6), when tolerably flat, and the margin of the 

 clypeus and the front are produced into a broad border ( Copris, Ontho- 

 pliagus, Ateuchus} ; TURRETED (c. turritum, PI. IV. f. 7)> when it is 

 produced anteriorly and above into a pyramidal point (Truxafcs). 

 We have already mentioned HORNED (c. cornulum) and ROSTRATE 

 (c. rostraium) heads. A head furnished with swollen cheeks is called 

 BUCCATE (c. buccatum, PL IV. f. 1, Myopa). 



With respect to the differences of the masticating organs themselves, 

 we shall proceed as we did in their description, by taking them 

 consecutively. 



The upper lip, or labrum, differs as to its figure, surface, margin, 



