MOUTH-PARTS OF INSECTS. 318 
There are three pairs of mouth-appendages : first, the true 
jaws or mandibles (Fig. 273), which are single-jointed, and 
are broad, short, solid, with a toothed cutting and grinding 
edge, adapted for biting. The mandibles are situated on 
each side of the mouth-opening. Behind the mandibles 
are the maxille (Fig. 273), which are divided into three 
lobes, the inner armed with teeth or spines, the middle lobe 
unarmed and spatula-shaped, while the outer forms a five- 
jointed feeler called the mazxillary palpus. The maxille are 
accessory jaws, and probably serve to hold and arrange the 
food to be ground by the true jaws. The floor of the mouth 
is formed by the ladiwm (Figs. 273 and 274), which in real- 
ity is composed of the two second maxille, soldered together 
in the middle, the two halves being drawn separately in Fig. 
273; to each half is appended a three-jointed palpus. 
Within the mouth, and situated upon the labium, is the 
tongue (lingua), which is a large, membranous, partly hol- 
low expansion of the base of the labium ; it is somewhat 
pyriform, slightly keeled above, and covered with fine, stiff 
hairs, which, when magnified, are seen to be long, rough, 
chitinous spines, with one or two slight points or tubercles 
on the side. These stiff hairs probably serve to retain the 
food in the mouth, and are, apparently, of the same struc- 
ture as the teeth in the crop. The base of the tongue is 
narrow, and extends back to near the pharynx (or entrance 
to the gullet), there being on the floor of the mouth, behind 
the tongue, two oblique slight ridges, covered with stiff, 
golden hairs, like those on the tongue. 
The internal anatomy may be studied by removing the 
dorsal wall of the body and also by hardening the insect 
several days in alcohol and cutting it in two longitudinally 
by a sharp scalpel. 
The esophagus (Fig. 276, @) is short and curved, contin- 
uous with the roof of the mouth. There are several longi- 
tudinal irregular folds on the inner surface. It terminates 
in the centre of the head, directly under the supra-cesopha- 
geal ganglion, the end being indicated by several small coni- 
cal valves closing the passage, thus preventing the regurgita- 
tion of the food. The two salivary glands consist each of a 
