552 INSECTA ORDER COLEOPTERA. 



rapidly exterminated in nearly all parts of the world by cultivation, clearing 



of forests, drainage, etc.; and there is good reason to he- 

 Extermination of lieve that a large proportion of the insects now existing will 

 Species. become extinct before they ever find a place in our museums 



at all. The extermination of small animals proceeds pari 

 passu with that of larger ones ; but is rarely noticed, as their existence is, for 

 the most part, unknown and unsuspected. 



Insects generally pass through four stages, called egg, larva, pupa, and 

 imago. In some orders, the pupa is inactive, and the insect is then said to 



have a perfect metamorphosis. In other orders, the pupa 



Metamorphoses only differs from the larva by possessing wing-cases, and 



of Insects. continues to feed as before. Then the metamorphoses are 



said to be incomplete. The egg is laid by the parent insect 

 on or near the appropriate food of its progeny, which, in insects with perfect 

 metamorphoses, is nearly always very different from that of the perfect 

 insect. The larva is frequently called a grub, maggot, or caterpillar, and is 

 generally more or less worm-like. It may be legless, or may possess several 

 pairs of legs, as well as the six pairs analogous to those of the perfect insect. 

 In insects with imperfect metamorphoses, the larva and pupa much resemble 

 the perfect insect ; and their food is frequently nearly similar. When 

 insects reach their final stage, they generally acquire wings, and become 

 capable of perpetuating their species. There are, however, numerous insects 

 which never acquire wings ; and in other cases the wings are undeveloped in 

 one sex, generally the female. 



In the perfect state, an insect consists of a number of rings, called seg- 

 ments, or somites, agglutinated into three masses, called the head, thorax, 



and abdomen, which can generally be well distinguished. 

 Head of Imago. The head is considered to consist of a number of somites, 



jusfc as the skull of vertebrate animals is thought to con- 

 sist of a number of modified vertebrae. The head contains several of the 

 most important organs of the senses, such as the compound facetted eyes on 

 each side of the head ; the antennae, two long jointed organs, often feathered, 

 or knobbed at the extremity, which are generally inserted in front between 

 the eyes ; the ocelli, stemmata, or simple eyes, of which there may be one, 

 two, or three, on the crown of the head ; and the mouth, which is either fur- 

 nished with mandibles for biting, or a proboscis for sucking. There are also 

 two pairs of jointed organs projecting in front of the mouth, called labial and 

 maxillary palpi ; but one or other pair is frequently wanting. 



The three segments behind the head are called the thorax. Each of these 

 bears one pair of legs beneath, and the second and third pairs bear the wings 



at the sides ; for most insects have four wings and six legs 

 Thorax. in the perfect state. The legs are composed of several parts, 



called the coxse, or hips ; the trochanters, or hinge-joints ; 

 the femora, or thighs ; the tibise, or shanks ; and the tarsi, or feet. The 

 tarsus is composed of five or fewer joints, known as the joints of the tarsi. 

 The abdomen is composed normally of nine segments, exclusive of some 

 smaller ones at the extremity in connection with the appendages of the 

 generative system ; but there are often fewer visible. Insects breathe by 

 tracheae, tubes which open by spiracles on the sides of the body. Many in- 

 sects are furnished with stridulating organs in the abdomen, while others 

 stridulate by means of various structures on their legs and wings ; and in 

 some insects the organs of hearing are situated on the legs. 



