STRUCTURE, METAMORPHOSES, ETC., OP COLEOPTERA. 21 
examined they require to be carefully dissected; this 
is by no means a difficult operation ; if we examine the 
under side of the head of any beetle, we shall find that 
nearer to or further from the front there is a suture ; 
this suture is called the mental suture, or more 
generally, though erroneously, the gular suture; the 
true gular sutures, however, are situated at each side 
of the mental suture ; now if with a needle (ground 
down to an edge on a fine hone and fixed by sealing- 
wax into a piece of wood such as a match stem) we 
divide this mental suture, and in the case of a larger 
insect the gular sutures as well, we shall be able to 
separate and examine in detail all the mouth organs ; 
as a rule, when the mental suture is severed, the 
montum, labium, and maxillae may at once be removed 
in one piece, and may afterwards be easily separated, 
especially if a little water is spread over them by a 
camel's-hair brush : for dissecting small insects a lens 
mounted on a stage is very useful, or, if it can be pro- 
cured, a Zeiss’s dissecting microscope, or any micro- 
scope that leaves the hands free and does not invert 
the imago of the insect. 
The compound microscope is often indispensable for 
the mere superficial examination of exceedingly small 
beetles ; and such points as the sexual characters, form 
and number of the joints of the tarsi and palpi, &c., 
aro best seen under it when damped with clean water 
or benzine, or carbolic acid and spirits of wine mixed 
in the proportion of one to twenty. 
The scrutiny of specific characters is at once more 
general and more close than for any other purpose, and 
necessitates inspection and comparison of the form of 
many parts of the body ; the relative length and 
