INSECTS. 



[ 357 ] 



INSECTS. 



the labium or lower lip (PI. 26. fig. 2 i, I, m). 

 This consists of several parts : the most 

 posterior is the mentum (fig. 3 I), which is 

 articulated posteriorly with the gula (fig. 3 «)• 

 Sometimes an intermediate portion occurs, 

 the submentum (fig. 3 m), at others this is 

 consohdated with the occiput (fig. 2 m). The 

 most anterior portion is the ligula (figs. 2, 

 3 i), which is frequently notched or lobed ; 

 and is sometimes furnished with two lateral 

 portions called paraglossse (fig. 2*). Between 

 the ligula and the mentum or submentum 

 are the palpigers, one on each side (fig. 2i); 

 these are sometimes united, and to them 

 the labial palpi (figs. 2, 3 k) are attached. 

 Below the labrum are the mandibles, one on 

 each side, forming two strong curved jaws, 

 and frequently furnished with powerful 

 teeth (figs. 3 /, 22 b) ; these are the proper 

 organs of manducation. Below the mandi- 

 bles are two other lateral organs, the maxillae 

 (figs. \,2, 3g; fig. 22 c); they are usually 

 less firm than the mandibles, and serve to 

 hold and convey the food to the back of the 

 mouth. Each maxilla is furnished with a 

 jointed palp (figs. 1, 2, 3 h), and sometimes 

 with an appendage called the galea or 

 helmet (fig. 22*); and an inner curved and 

 acute portion termed the lacinia or blade 

 (fig. 22 1). In some insects there is a di- 

 stinct soft and projecting organ, forming the 

 floor of the mouth, the lingua or proper 

 tongue (fig. 22 d) ; the tongue of the cricket 

 (fig. 23) is a favourite and beautiful micro- 

 scopic object. 



These structures are best examined in the 

 Coleoptera or Orthoptera, in which the parts 

 we have described are most distinct. In the 

 other orders they are altered in structure to 

 adapt them to the nature of their food. 

 Thus in the Lepidoptera, the labrum and 

 mandibles are reduced to three minute tri- 

 angular plates ; the maxillae are elongated 

 to form the antlia (Antlia), at the base of 

 which a pair of minute palpi are often to be 

 detected. The labium is small, triangular 

 and furnished with a pair of large palpi 

 clothed with long hairs or scales, and serving 

 for the defence of the antlia. 



In the Hemiptera (PI. 26. figs. 26, 27), 

 the labrum is short and pointed, and over- 

 laps the root of the rostrum ; the mandibles 

 and maxillae are transformed into slender 

 lancet-like organs (the maxillarj^ palpi being 

 obsolete), enclosed within the equally elon- 

 gated horny and jointed rostrum or labium, 

 the labial palpi also being obsolete. 



In the Diptera (PI. 26. figs. 29, 30), 



the five upper organs, together with the 

 internal tongue, are elongated into lancet- 

 like organs, the maxillary palpi being 

 attached to the base of the maxillae. These 

 six organs are enclosed in a fleshy thickened 

 piece (the labium), often terminated by two 

 large lobes which act as suckers. In man}'^ 

 species, however, some of these lancet-like 

 organs are obsolete. This kind of mouth is 

 termed a. proboscis. 



These varieties are further noticed under the 

 heads of the genera selected for illustration. 



Behind the head we have the thorax. This 

 consists of three rings or pieces, each of 

 which supports a pair of legs (fig. 365, e, g, 

 k). The first ring is called the prothorax 

 {e), the second the mesothorax (g), and the 

 third the metathorax (k). Each of these 

 rings consists of a dorsal and a sternal piece ; 

 the dorsal half-rings are called the pro- 

 notum, mesonotum, and metanotum ; the 

 ventral or sternal, the prosternum, meso- 

 sternum, and metasternum. In the four- 

 winged insects, the anterior wings are 

 attached to the central piece or mesothorax 

 (g), the posterior wings to the metathorax 

 {k). In the Diptera, the wings are attached 

 to the mesothorax, and the halteres to the 

 metathorax. Various other subdivisions 

 have been made of these parts, but they are 

 too numerous to mention here. It may be 

 remarked, however, that the epimera are the 

 pieces to which the basal joints of the legs 

 are directly attached ; that the under part of 

 the thorax or pectus is sometimes furnished 

 with an elongated acuminate appendage, the 

 sternum; and that the scutellum or shield 

 is a piece existing at the upper and back 

 part of the mesonotum, and extending be- 

 tween the wings. 



The legs are placed on the under side of 

 the body, and are joined to its segments at 

 an articular cavity existing between the 

 sternum and the epimeron, called the aceta- 

 bulum. Each leg usually consists of five 

 parts. The first is the hip or coxa (PI. 28. 

 fig. 9 g) ; but sometimes there is a small, 

 very moveable piece between the epimeron 

 and the coxa (PI. 28. fig. 9, between^ and g), 

 called the trochantin; this is, however, gene- 

 rally absent or consolidated with the coxa. 

 The second joint is the trochanter (PI. 28. 

 fig. 9 h); it is mostly small, and annular. 

 The third is the thigh or femur (fig. 365 m ; 

 PI. 27. figs. 4, 5, 7 d), the thickest and 

 usually the largest joint of the leg. Next 

 comes the fom*th, the tibia (fig. 365 0; PI. 27. 

 figs. 4, 5, 6, 7 c)j which is thinner, usually 



