TNSECTA. 



889 



the lesser jaws, maxilla, in being articulated 

 both with the upper and under surface of the 

 head. 



The maxilla, or lesser jaws C/g.370,B,C), are 

 of very compound structure. They are situated 

 between the mandibles and labium, and are 

 employed by the insect to hold its food, and to 

 convey it to the posterior part of the mouth. They 

 are each formed of four primary and three or 

 more accessory parts, when mostcompletely deve- 

 loped. The primary parts are the cardo or hinge, 

 thestipes or footstalk, thepalpifer, and the lacinia 

 or blade. The accessory parts are the galea or 

 lobus superior; the lobus inferior, and unguis. 

 The cardo (fig. 370, B, C, 1) is the joint upon 

 which nearly all the motions of the maxilla 

 depend. In Hydrous it is a minute trapezoid 

 or irregularly triangular corneous plate, with an 

 elongated curved process by which it is arti- 

 culated with the os transversum on the under 

 surface of the cranium, and over which the 

 cardo is articulated like a hinge. In some 

 genera, as in Staphylinus, it is more elongated, 

 and this is particularly the case in Melolontha, 

 whence it was called branche transversale. In 

 most instances it is as it were wedged in 

 between the sub-mentum and mandible. It is 

 articulated at its anterior margin with the 

 second piece of the maxilla, the stipes ( % 2), 

 which forms the outer surface of the organ, 

 being considered its primary part. It is an 

 elongated corneous plate, broadest at its articu- 

 lation with the cardo. It is approximated 

 along its anterior margin to the squama palpifer 

 (3), a broad plate which covers the superior 

 external surface of the maxilla. Immediately 

 beneath the anterior margin or apex of the 

 squama is inserted the palpifer (4), a short 

 cylindrical appendage, which is usually con- 

 sidered part of the squama, the whole being 

 together called the palpifer. It supports the 

 proper maxillary or true palpus, which is re- 

 markable for its length in the Hydrous. The 

 lacinia (5), sometimes improperly called max- 

 illa, forms the internal portion of the organ, 

 and, as we shall hereafter see, appears in its 

 earliest condition in the embryo to constitute a 

 separate organ or appendage, belonging to the 

 mentum as the stipes appear to belong to the 

 sub-mentum but which in the course of deve- 

 lopment becomes approximated to the stipes to 

 form part of the maxilla of the perfect insect. 

 Like the stipes, it is a broad corneous plate, 

 which forms the greater portion of the under 

 surface of the maxilla, and is articulated with 

 the cardo only by a small portion of its base. 

 On its upper surface, which forms a great part 

 of the sides of the mouth, it is soft, membra- 

 nous, and covered with fine hairs. It gives 

 origin at its anterior truncated extremity to the 

 accessory parts of the maxilla, the lobus supe- 

 rior and inferior. The lobus superior, or galea, 

 is a thick, double-jointed organ (6), densely 

 covered at its anterior margin with stiff reddish 

 hairs. It is articulated with the external an- 

 gle of the lacinia, and covers the lobus inferior, 

 which is articulated with the internal angle, 

 and on this account, more particularly in 

 Orthoptera, is called the galea or helmet. It 

 is used by this and other insects as a palpus, 



or feeler, to touch and convey food to the 

 mouth. The lobus inferior is a short quadrate 

 joint (7), articulated with the internal angle 

 of the lacinia, of which it forms the proper 

 Continuation. At its superior extremity is a 

 minute articulated claw (8), densely covered 

 on its upper surface with long stiff hairs, as is 

 also the whole of the internal margin of the laci- 

 nia itself,which forms the lateral boundary of the 

 mouth, and is continuous with the soft lining 

 of the pharynx. The maxillary palpi (A) are 

 two very long flexible organs, composed each 

 of four joints. The palpifer, upon which they 

 are situated, is a short joint or tubercle, in- 

 serted at the anterior external angle of the 

 maxilla, between the angle of the lacinia and 

 the plate which covers the superior surface of 

 the maxilla (3), and of which it forms a part, 

 but from which in this insect it appears quite 

 distinct. The first joint of the palpus is ex- 

 ceedingly short, so as to allow of extensive 

 motion to the organ in every direction, while 

 the second is much longer than in most other 

 insects, and, when the palpus is retracted, 

 forms with the third joint a distinct elbow or 

 bend. The third and fourth joints are also of 

 great length, so that the insect is enabled to 

 protrude the organ to a great distance. The 

 labial palpi (jig- 369, /:) are much shorter than 

 the maxillary. The first two joints are very 

 minute, the second being partly hidden within 

 the first, but the third and fourth are long and 

 projecting, but not so long as those of the 

 maxillary palpi. 



From all we have been able to observe, the 

 office of the maxilla appears to be of a two- 

 fold kind, and of greater importance to the 

 insect than that of the mandibles themselves. 

 The chief office is that of seizing and retaining 

 the food within the mouth ; and the secondary 

 that of assisting the mandibles in comminuting 

 it before it is passed on to the pharynx. Con- 

 sequently all the parts of the maxilla are sub- 

 ject to great variation of form ; and in the dif- 

 ferent tribes of Coleoptera, as in the other 

 orders of insects, each particular form is 

 adapted to the kind of food on which the in- 

 sect subsists. In Melolontha, in which the 

 four primary parts, the cardo, stipes, palpifer, 

 and lacinia, were first accurately distinguished 

 by Straus Durckheim,* the maxilla is a thick 

 obtuse organ, with the cardo, which is less 

 completely developed in Hydrous than in most 

 other insects, forming a broad transverse piece, 

 the stipes a short and triangular one, the pal- 

 pifer also nearly triangular, and the lacinia, 

 which, as Straus has remarked, is always con- 

 tinuous with the pharynx, nearly also of a tri- 

 angular form, and together constituting a thick 

 compact organ, with its inner angle, the lobus 

 inferior in other insects, forming a strong pro- 

 jecting inarticulated tooth, and its external, 

 articulated with a short thick galea, armed 

 with three obtuse points, which probably serve 

 the office of teeth for masticating the paren- 

 chymatous food of this species. This form of 



* Considerations Generates sur 1'Anatomie Com- 

 paree des Animaux Articules, par Hercule Straus- 

 Durckheim, 1828, p. 68, pi. i. fig, 8. 



