GARDEN PESTS IN NEW ZEALAND 



few cases), the only appendages being those connected with reproduc- 

 tion; the latter are well developed in the female weta, where the egg- 

 laying apparatus, or ovipositor, projects blade-like from the apex of 

 the abdomen. In very many insects, however, the external -reproductive 

 organs are not readily seen without special study. 



All insects, from the largest to the most minute, contain internally 

 a well-formed heart and a digestive, reproductive, respiratory, and 

 nervous system (Fig. 3), while the spaces surrounding these organs are, 

 for the most part, packed with a complex system of muscles. The 

 heart is a delicate tube lying along the middle of the back or dorsal 

 surface of the body, immediately under the skin, and extends almost 

 from one end of the insect to the other; in an almost similar position, 

 close to the lower or ventral surface of the body, the nervous system is 

 situated, and consists of a chain of nerve centres, or ganglia, connected 

 by a double nerve cord, the most anterior of these ganglia being in the 

 head and forming the brain, the following three lying in thei thorax, 

 one to each segment, while the remainder are confined to the abdomen, 

 one ganglion to each segment, as in the thorax. In many insects the 

 number of nerve centres is reduced, owing to the fusion of two or more. 

 The reproductive organs are located in the abdomen. 



The digestive system consists of a tube (Fig. 3), with its append- 

 ages, opening at the mouth and at the posterior end of the body; this 

 alimentary canal may be straight and simple, or convoluted and complex, 

 according to the insect and the nature of its food. Respiration in 

 insects is carried on by means of a system of air tubes (Fig. 3), which 

 branch and re-braneh to form an intricate system of delicate tubular 

 airways, carrying the atmosphere to all tissues of the body ; the main air 

 tubes open at the surface by a series of breathing pores normally 

 arranged along each side of the body, except on the head; these pores 

 are best seen on a caterpillar or o i the abdomen of adult insects. 



