BREATHING. 



Fig. 5 



Breathing-tubes of 

 maggot of Warble Fly, 

 maa,nitied. 



■simiDle lips guarding the breathing opening, to the 

 more compound form in which they may be found 

 borne on short branched stalks 

 placed on each side near the 

 head of the larva, as is notably 

 the case with various kinds of 

 plant-stem-feeding fly maggots. 

 The various air-tubes {tra- 

 chece) start from each spiracle, 

 and then by means of branches, 

 which often join so as to form 

 a net-work, they carry the air 

 through every part of the insect, 

 — limbs, body, and intestines. 

 Insects do not draw in air 

 through one mouth, as we do ; 

 neither have they lungs, but 

 (commonly by means of the 

 spiracles) the air-tubes bring 



the action of the air to bear on the fluid answering to 

 blood, which fills the hollow body of the insect. This 

 fluid is not conveyed in veins, in the same manner as 

 with us ; but circulation is carried on by means of a 

 long vessel, which may be compared to a long heart, 

 lying down the middle of the back of the abdomen. 

 This vessel is divided by constriction into successive 

 chambers, and is furnished with slits at the sides. 

 Through these slits the blood-fiuid, which lies freely 

 in the cavity around, enters the so-called heart, and 

 by contraction or a kind of pulsation pushing it from 

 the hinder part of the vessel, the blood is driven along 

 it to a kind of aorta near the head. From this aorta 

 it is stated to pour freely into the body cavity, and 

 return in streams to the heart. Thus the main part 

 of the circulation is carried on, whilst air is conveyed 

 to the fluid by the passage of the breathing-tubes or 

 tracheae through the fluid.* 



* The above short and general description of the main principle 

 of the circulation is chiefly taken from Claus and Sedgwick's ' Text- 



