INSECTS. 



[ 431 ] 



INSECTS. 



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

 with an appendage called the galea or 

 helmet (fig. 22 *), and an inner cm-ved 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 moutli, 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 most of 

 these parts are 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 maxillcTS 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. 33. figs. 26, 27), 

 the labrum is short and pointed, and over- 

 laps the root of the rostrum ; the mandibles 

 and maxillce are transformed into slender 

 lancet-like organs (the maxillary 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. 33. 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 maxillte. These six organs are 

 enclosed in a fleshy thickened piece, the 

 labium, often terminated by two large lobes 

 which act as suckers. In many 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 illustra- 

 tion. 



Behind the head is the thorax. This 

 consists of three rings or pieces, each of 

 which supports a pair of legs (fig. 361 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 metasteraum. In the four- 

 winged insects, the anterior wings are 



attached to the central piece or mesothorax 

 (//), 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 kffs (usually called feet) are placed 

 on the underside of the body, and are joined 

 to its segments at an articular cavity exist- 

 ing between the sternum and the epimeron, 

 called the acetabulum. Each leg usually 

 consists of five parts. The fu'st is the hip 

 or coxa (PI. 35. fig. 9 r/) ; but sometimes 

 there is a small very moveable piece between 

 the epimeron and the coxa (PI. 3o. fig. 9, 

 between / and g), called the trochantin ; 

 this, however, is generally absent or con- 

 solidated with the coxa. The second joint 

 is the trochanter (PI. 35. fig. 9 k) ; it is 

 mostlv small, and annular. The third is the 

 thigh''or femur (fig. 361 m ; PI. 34. figs. 4, 

 5, 7 d), the thickest and usually the largest 

 joint of the leg. Next comes the fourth, the 

 tibia (fig. 361 o ; PI. 34. figs. 4, 5, 6, 7 c), 

 which is thinner, usually compressed, and 

 frequently furnished with spines, spurs, or 

 other appendages, especially at its end ; in 

 the ant the tibiae have each a beautiful 

 pectinate process. The last portion is the 

 foot or tarsus (fig. 361 p ; PI. 34. figs. 6,7 a), 

 which consists of several joints arranged in 

 a row. The number of these joints varies in 

 different insects ; sometimes it is different 

 in the anterior and posterior pairs of legs ; 

 they are, however, most commonlv five. 

 The last joint of the tarsus is usually fur- 

 nished with appendages, in the form of 

 hooks or claws, mostly two, and frequently 

 serrated, especially near the base. Some- 

 times also it has two or three delicate mem- 

 branous or fleshy cushions, called pulvilli 

 (PI. 34. figs. 7 & 8). ; these are more or less 

 covered with hairs, which are sometimes 

 terminated by little disks (fig. 9), and by 

 which it is supposed that the insects are 

 enabled to ascend or adhere to polished 

 surfaces in opposition to gravity. In other 

 insects elegant brush-like appendages are 



