HEXAPODA. 



57 



This hardening of the body-wall is not continuous, but 

 takes place in a series of more or less regular, ring-like bands, 

 which give the well-known seg- 

 mented appearance characteristic of 

 insects, and the animals closely Fig. 68.— a Larva, 



allied to them. Between the hardened ring-like segments 

 the body-wall remains soft and flexible. In this way provi- 

 sion is made fcr the various motions of 

 the body. The ring-like nature of the 

 segments of the body is best seen in 

 larvae (Fig. 68), and in the hinder part of 

 an adult insect (Fig. 69). The movements 

 of the legs, antennae, and certain other 

 appendages are provided for in the same 

 way ; each one is a cylinder made up of 

 several segments, and between these seg- 

 ments the wall of the cylinder remains 

 flexible. 



When a single segment of the body is 

 examined, the hardened portion is not 

 found to be a continuous ring, but is seen 

 to be made up of several portions more 

 Pig. 69.— a Mole Cricket, or less movable upon each other. Such 

 a hardened portion of the body-wall is termed a sclcrite 

 (scle'rite). 



The sclerites constitute the greater part of the body-wall, 

 the soft membranous portions separating them being in 

 most cases narrow. Usually these narrow portions are 

 mere lines ; they are then called sutures (sut'urs). 



Frequently the sutures become entirely effaced. We 

 are therefore often unable to distinguish certain sclerites in 

 one species of insect which we know to exist in another. 

 In such cases the effaced sutures are said to be obsolete. 



If the central portion or thorax of an adult insect be 

 examined, numerous sclerites and sutures can be observed 

 (Fig. 70). 



