COMMON BRITISH INSECTS. 



laid on a glass slide. I have now before me a pre- 

 paration of the tracheae of a silkworm which I made 

 twenty-two years ago, and it is not the least damaged 

 by keeping. 



These tracheae afford a most important character- 

 istic of the insects, inasmuch as the Crustacea do not 

 possess them at all, and the Arachnida generally, 

 though not always, breathe by means of internal air- 

 sacs. 



Next, the creature must be divided into three 

 distinct portions. This is the signification of the title 

 Insect, which is derived from two Latin words, signi- 

 fying cut-into, while the familiar Greek name of 

 Entoma (from which the word entomology is formed) 

 has precisely the same signification. This is, perhaps, 

 the most important of all the characteristics, as in the 

 Crustacea and Arachnida the head is merged into the 

 thorax, so that they are divided into two portions 

 instead of three ; while in the Myriapoda and Annelida 

 there is no distinct thorax, and sometimes scarcely a 

 distinct head. 



Next we come to the transformations which 

 insects have to undergo before they reach their perfect 

 or adult state. All animals really undergo a course 

 of transformation, but in the insect they take four 

 very distinct forms ; namely, the Egg, the Larva (i.e. 

 caterpillar or grub), the Pupa (or chrysalis), and the 

 imago, or perfect insect. Any of my readers who 

 have bred silkworms will be practically acquainted 

 with this fact, and will also know that the larva 

 changes its skin, or moults, several times before it 

 assumes the pupal form. The reason for this casting 



