BREATHING. 6 



formed of a succession of rings or segments ; and they 

 do not breathe, as we do, by drawing air through their 

 mouths into their lungs, but by branched tracheae, 

 that is, b}^ branched air-tubes running through all 

 parts of the structure, and furnished with little 

 openings at the outer end, mostly along the side 

 of the insect, through which the air supplies are 

 obtained. 



Let us go over this point by point. Insects not 

 having any bones, that is not having an inside 

 skeleton, need an outside skeleton or support to keep 

 them together. This is formed of a succession of 



Fig. 3. — Wireworm, nat. size aud magnified. 



rings or segments, often of a horny texture, as you 

 may see in a Wasp when it has been crushed on a 

 window-pane ; and the rings appear to be commonly 

 about thirteen in number. One of these rings* forms 

 the head, the three next support the legs and wings, 

 and the remaining rings or segments form the abdo- 

 men, and contain a portion of the organs of digestion 

 and those of reproduction. Thus an insect is formed 

 of rings : it is, scientifically speaking, annulose. In 

 the maggot or caterpillar stages, the rings or segments 

 are sometimes horny, as in the Wireworm (Fig. 3), 

 or soft, as with many kinds of caterpillars (Fig. 1) ; 

 and in the chr^^salis state they are often only slightly 

 observable. 



* The absolute uumber of segments has been a subject of much 

 discussion ; at one time they were considered to be typically thirteen ; 

 following on this it was considered that the three segments of the 

 thorax were each typically composed of four lesser segments, aud now 

 it is given on good authority that the head segment is composed also 

 ■of four smaller ones. 



