CLASS IXSECTA. 



45 



either the liver or the kidneys. The intestine opens into 

 a large chamber (c), which opens upon the surface by a 

 distinct vent (v). 



Fig. 1 8. — Diagram of the anatomy of an insect, an Antennae ; e Eye ; m 

 Mouth ; g Gullet ; sg Salivary gland ; s Stomach ; / Tubes supposed to 

 represent the liver ; i Intestine ; c Chamber into -n-hich the intestine 

 opens ; v Vent ; h Heart ; n Nervous system ; I Bases of the legs. 



The nervous system (fig. i8, n) consists of a chain of 

 little nervous masses placed in pairs along the lower sur- 

 face of the body, a pair of these masses being situated in 

 each ring of the body. The first pair of nervous masses 

 is placed above the gullet, and the second pair behind or 

 below the gullet, and the cords which vinite these two 

 pairs pass on the sides of the gullet. It follows from 

 this that the gullet is surrounded by a ring or "collar" of 

 nervous matter. 



The heart is in the form of a long tube (h), placed along 

 the back, and furnished with flaps or valves, which only 

 allow the blood to pass in one direction, namely, towards 

 the head. 



The breathing-organs are in the form of branched tubes, 

 which commence on the surface of the body in little 

 rounded openings, and then branch freely through the 

 tissues, thus conducting the air to all parts of the body, 

 and purifying the blood. The breathing-tubes are com- 

 posed of a delicate membrane, the walls of which are sup- 

 ported by a horny fibre, which is coiled up in the interior 

 in the form of a close spiral. 



WTien young, the Dragon-fly is very diff'erent to the 

 grown-up insect, and it passes through certain changes, 



