96 THE LARVA OB NYMPH [CH. 



a considerable time before. The beginning of this change is 

 marked by an alteration in the colour and behaviour of the larva. 

 The colour darkens considerably, greenish larvae becoming a dull 

 opaque brown. The larva becomes listless and refuses to feed. 

 A rapid proliferation of the hypoderm cells, preparatory to the 

 formation of the imaginal exoskeleton, causes the larva to appear 

 tense and swollen. In particular, the thorax swells up so that 

 the wing-sheaths stand vertically off from the abdomen. This is 

 partly due to the growth of the great wing-muscles, partly also 

 to increased growth of the pleurae forcing the meso- and meta- 

 notum backwards into an oblique position. The compound eyes 

 begin to swell, owing to rapid formation of new separate elements. 

 The imaginal hypodermis and cuticle soon begin to shew through 

 the larval skin, and are generally pinkish in colour. Soon the 

 gills cease to be functional. At the same time, the thoracic 

 stigmata, either of one or both sides, become functional, and the 

 larva takes up a position with its head and part of its thorax 

 protruding from the water, so as to breathe air directly. 



The emergence of the imago was first described by Reaumur [129], 

 whose beautiful account has never been excelled. Numerous sub- 

 sequent writers have described and figured the process accurately 

 in the case of an Aeschnine, Libelluline or Agrionid Dragonfly. 

 We have here introduced a touch of novelty by figuring the 

 emergence of Petalura gigantea (fig. 43), which differs from the 

 more usual type in several very interesting points. The descrip- 

 tion, however, will be general, the peculiarities of Petalura and other 

 genera being noted by the way. 



As soon as the internal changes are practically complete, the 

 larva climbs out of the water, usually up a stick, rock, reed-stem 

 or other suitable object. Some species climb to a considerable 

 height, but most of them only travel from a few inches to a yard. 

 Many larvae (Gomphinae and some Libellulidae] cannot climb, and 

 just crawl out of the water up a shelving beach. They are 

 sometimes compelled to emerge when only partly out of the water. 

 Petalura, which forms burrows or canals in the peat or mud of 

 small mountain-swamps (Plate IV, fig. 1), hauls itself out of its 

 hole (A) by means of its legs, and ascends a convenient reed-stem 

 for about a foot. It is thickly coated with mud. 



