42 OUTLINES OF NATURAL HISTORY. 



CHAPTER XII. 



CLASS INSECTA. 



The true Insects derive their scientific as well as their 

 ordinary name from the distinctness with which the body- 

 is cut or divided into distinct portions or regions (Latin, 

 inseco, I cut into). Of the many excellent representatives 

 of this class which might be selected, none, perhaps, is 

 l^etter than one of the larger Dragon-flies, such as the great 

 ^shna grandis of Britain (fig. 17, A). 



If we look at a Dragon-fly, we observe very readily that 

 the body is more or less clearly di\dded into three portions, 

 a head in front, a chest (or "thorax") in the middle, and 

 a tail (or "abdomen") behind. It will also be seen that 

 the body is composed of a number of rings or "segments," 

 which are placed one behind the other. These segments 

 are very conspicuous in the tail or abdomen (fig. 17, A, 

 a), are less conspicuous in the trunk or " thorax," and can- 

 not be clearly discerned at all in the head. 



The entire skin is hardened with horny matter, so that 

 each ring or segment forms a more or less resistant tube, 

 within which the internal organs are protected. 

 _ Commencing with the head (fig. 17, A, h), no distinct 

 rings can, as already remarked, be clearly made out ; but 

 nevertheless the head really consists of a certain number 

 of segments consolidated into a single mass. Upon its 

 sides, the head has two conspicuous shining globes (fig. 1 7, 

 D, e e), which are the eyes. Each eye is what is termed 

 " compound," being reaUy composed of an enormous 

 nmmber (several thousands) of minute eyes placed side bj^ 

 side, and doubtless conferring upon the creature a high 

 power of vision. Besides these compound eyes, the head 

 likewise carries three "simple" eyes, which are so minute 

 as only to be visible with a magnifying glass. The head, 

 further, carries upon its upper surface two jointed thread- 



