4 NEW ZEALAND ENTOMOLOGY. 



The wings are attached to the meso- and metanotum ; 

 they consist of two membranes traversed by numerous 

 horny ribs (Fig. I. iW and 2W). 



The abdomen is made up of nine segments (C 1 to 9), 

 some of which are not infrequently wanting. It contains 

 the organs of nutrition, circulation, and generation. 



The digestive system, the structure of which is apparent 

 from Fig. II., consists of the following divisions : the throat, 

 or oesophagus (8) ; the crop (9) ; the gizzard, or proventri- 

 culus (10) ; the pancreas (1 1 1 1) ; the stomach, or ventriculus 

 (12); the biliary vessels (13 13 13) ; the ilium, or little gut (14 

 14) ; and the colon (15) ; ending in the anus (16). In the 

 suctorial tribes, the crop is modified into a very peculiar 

 organ, termed the sucking stomach, which presents itself as 

 a small bag, attached to the throat by a thin tube. This 

 bag exhausts the air from the throat, when the insect is 

 sucking, thus producing a vacuum therein, and causing 

 a rapid ascent of fluid into the stomach. 



The heart of insects consists of an elongated tube lying 

 along the back, and termed the dorsal vessel. It is com- 

 posed of a variable number of chambers, the blood being 

 driven forward towards the head by its contractions. These 

 motions may be easily seen in transparent species. 



The breathing organs are distributed throughout the 

 body in the form of numerous minute air-tubes, which are 

 supplied with air from a variable number of apertures, situ- 

 ated on the sides of the insect, and termed spiracles. 



The nervous system consists of a chain of ganglia, run- 

 ning down the ventral surface of the insect, and analogous 

 to the spinal cord of higher animals. The number of ganglia 

 varies greatly among the different tribes. 



The metamorphosis of insects, which I have previously 

 mentioned as one of their most essential attributes, consists 

 of four distinct stages, viz., the Egg, Larva, Pupa, and 

 Imago. 



