MOUTH-PARTS OF INSECTS. 513 



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 maxillae (Pig. 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 maxillary palpus. The maxillffi are 

 accessory jaws, and jjrobably serve to hold and arrange the 

 food to be ground by the true jaws. The floor of the mouth 

 is formed by the laMum (Figs. 273 and 274), which in real- 

 ity is composed of the two second maxillae, 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 niouth, 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 cesophagus (Fig. 276, ce) 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 



