1890.] ENTOMOLOGICAL NEWS. 87 



body. If such a young larva be examined* the jointed appear- 

 ance of the exterior will be seen. The skin of this young larva 

 is quite soft, but becomes harder as the larva grows. This hard- 

 ening is due to the deposition in the outer layer of the skin 

 (called the cuticle) of a horny substance — chitine. The chitine is 

 deposited in the cuticle of the different segments, but there is 

 left a narrow space around the body between each segment, in 

 which there is little or no chitine. These narrow rings of unaf- 

 fected skin divide the segments from each other, and are termed 

 sutures. Remaining soft, the sutures permit a freedom of motion 

 of the hard segments upon each other. 



In larvae the sutures are usually wider than in the correspond- 

 ing imagos. Very often the sutures themselves become hardened 

 by chitine, so that the line of separation between two segments 

 disappears. Such an obliteration of sutures occurs very fre- 

 quently in the head and fore-parts of imagos, and less frequently 

 in the hind parts. 



We have spoken of the segments as hard, but the hard part 

 of any one segment is not a continuous ring. On the contrary, 

 the hard part of a segment consists of several pieces which are 

 more or less free to move upon each other. These pieces are the 

 sclerites (from the Greek skleros, hard). Some of the soft cuticle 

 remains between the sclerites, and this separating portion also 

 receives the name of suture, and like an inter-segmental suture 

 may also become "obsolete" (/. e. obliterated). 



The skin, originally soft, but now with its cuticle hardened in 

 the segments, the hard part of each segment consisting of several 

 sclerites, forms the body-wall of the Insect. 



The reader of this series already knows that all an insect's 

 growth is completed in its larval state. As a larva grows quite 

 rapidly, and as chitine is being constantly deposited in the cuticle, 

 the cuticle thus hardened loses its elasticity and is soon too small 

 for the increasing size of the body. Consequently it splits along 

 the middle line of the back, and through this fissure the insect 

 withdraws itself from its chitinous coat. Or, in other cases, the 

 cuticle comes off gradually in thin shreds. The "new skin" 

 contains very little chitine as yet, and being quite elastic, stretches 

 to accommodate the size of the body. This skin (cuticle) in turn 



* The student cannot be too strongly reminded that he should compare 

 these papers with some insect, say a grasshopper. 



