42 INSECT TRANSFORMATION 



of the abdomen a pair of strong un jointed appendages are 

 present in both sexes ; these are especially large in the male, 

 which uses them in pairing, in conjunction with one or two 

 lower processes which are wanting in the female. 



The digestive system (Fig. 25 A) of a dragon-fly has the 

 same parts and the same general arrangement as that of a 

 grasshopper ; the stomach (mg), however, is relatively longer 

 and the intestine (hg) relatively much shorter, for the whole 

 food-canal runs a straight course from mouth to anus, such 

 abbreviation being a well-known modification in animals 

 which live on flesh-food rather than on vegetable matter. 

 In the nervous system (Fig. 26 A) the great brain (br), with 

 its strongly-developed optic ganglia (0g),is noteworthy. The 

 thoracic ganglia (tg, i, 2, 3) are close together, the first ab- 

 dominal (ag i) being almost in contact with the third thoracic, 

 and being followed by a chain of seven other abdominal 

 ganglia (ag 2-8). The large compound eyes have already 

 been mentioned, and dragon-flies are said to be more far- 

 sighted than any other insects. In correlation with their 

 powerful flight and high activity, dragon-flies have especially- 

 developed breathing organs. Large paired dorsal and ventral 

 trunk air-tubes (Fig. 25 A, dt, vnt) run along the body, from 

 head to tail, and there are also a pair of visceral trunks (vt) 

 lying alongside the food-canal. The tubes receive the air 

 supply through ten pairs of lateral spiracles, a pair on the 

 mesothorax, a pair on the metathorax, and a pair on each 

 abdominal segment from the first to the eighth inclusive 

 (Fig. 25 A, sp). The whole build of a dragon-fly the mobile 

 head with its great eyes and strong jaws, the spiny legs, the 

 long, firm wings, the well-poised hind-body suggests adapta.- 

 tion for life in the air. 



Turning to the life-history of such an insect, we are struck 

 by the fact that its early stages are passed under water, and 

 thus it is clear that the conditions amid which the young 

 creature lives must be very different from the aerial sur- 

 roundings of the winged adult, and it is evident that its body- 

 form must differ correspondingly. It has already been 

 mentioned that some female dragon-flies lay their eggs in slits 

 cut by the ovipositor in the tissues of aquatic plants, while 

 others simply drop them into the water. The embryonic 



