41 8 NEUROPTERA 



metallic tints, while sometimes the two sexes of one species have 

 differently coloured wings. The smallest and most delicate 

 dragon-flies that are known are found in the tropics ; some of 

 the genera allied to Agrion consist of Insects of extraordinary 

 fragility and delicacy. 



Although the mature Odonata are so pre-eminently endowed 

 for an aerial and active life, yet in the earlier stages of their 

 existence they are very different ; they are then, without excep- 

 tion, of aquatic habits ; though carnivorous also in this period 

 of their existence, they are sluggish in movement, lurking in 

 concealment and capturing their prey by means of a peculiar 

 conformation of the mouth, that we shall subsequently describe. 

 Their life-histories are only very imperfectly known. 



The eggs are deposited either in the water or in the stem of 

 some aquatic plant, the female Insect occasionally undergoing 

 submersion in order to accomplish the act. The young on 

 hatching are destitute of any traces of wings (Fig. 265), and the 

 structure of the thoracic segments is totally different from what 

 it is in the adult, the rectal respiratory 'system (Fig. 265, x), to 

 which we shall subsequently allude, being, however, already present. 

 The wings are said to make their first appearance only at the third 

 or fourth moult. At this time the pleura of the second and third 

 thoracic segments have grown in a peculiar manner so as to form 

 a lateral plate (Fig. 266, B, shows this plate at a later stage), and 

 the wing-pads appear as small projections from the membranes at 

 the upper margins of these pleural plates (Fig. 266, A, B). The 

 plates increase in size during the subsequent stadia, and meet 

 over the bases of the wing-pads, which also become much longer 

 than they were at first. The number of moults that occur during 

 growth has not been observed in the case of any species, but they 

 are believed to be numerous. There is no pupa, nor is there any 

 well-marked quiescent stage preceding the assumption of the 

 winged form at the last ecdysis, although at the latter part of its 

 life the nymph appears to be more inactive than usual. When full 

 grown, the nymph is more like the future perfect Insect than it was 

 at first, and presents the appearance shown in Figs. 266 and 270. 

 At this stage it crawls out of the water and clings to some sup- 

 port such as the stem or leaf of an aquatic plant ; a few minutes 

 after doing so the skin of the back of the thoracic region splits, 

 and the imago emerges from the nymphal skin. The nymphs 



