46 INSECT TRANSFORMATION 



so that it may be bitten up and devoured. Hence the larva 

 is, like the adult, a predaceous creature, but the adaptation 

 for securing victims is widely different, for while the adult 

 catches flies as it skims through the air, the larva rests in its 

 watery home as a comparatively sluggish stalker, waiting, with 

 mask folded beneath the head, for a suitable prey to pass by 

 its lair. 



Through a series of ten to fourteen moults the young larva 

 grows towards the adult condition ; the time occupied by these 

 changes may be one or two in some cases even three to five 

 years. The compound eyes increase in size and in the 

 number of their facets after each moult, but the ocelli do not 

 appear until the latest stages. The mesothorax and meta- 

 thorax increase in size while the prothorax remains relatively 

 small ; after the second moult each foot becomes two- 

 segmented, and somewhat later (Fig. 24) the third segment 

 is added. Wing-rudiments (Fig. 24 A C, W2, w$] are clearly 

 visible about the fifth stage, and these become larger after 

 each moult ; they are triangular in form lying obliquely over 

 the front of the abdomen, and so arranged that the hindwing 

 overlaps the forewing on each side. Thus it comes to pass 

 that the upper surface of the larval wing-rudiment becomes 

 the lower surface of the developed wing in the adult dragon-fly. 



With regard to the internal organs of the larvae, it may be 

 noted that the ganglia of the central nervous system are 

 relatively very large and very close together in the newly- 

 hatched insect (Fig. 26 B). As growth proceeds the nerve- 

 cords lengthen so that the ganglia, hardly increasing in size, 

 become far apart from one another. The digestive system of 

 the larva shows the same general arrangement as that of the 

 imago, but the mid-gut is relatively shorter and the hind-gut 

 longer. In larvae of the larger and more robust dragon-flies, 

 the central region of the hind-gut is enlarged and specialized to 

 form the curious breathing organ known as the branchial 

 basket. 



In this remarkable structure we see one of the special adap- 

 tions necessary for the dragon-fly larva's life under water. In 

 the aquatic habit of its larva, a dragon-fly resembles many 

 other insects of various orders, and the diverse modifications 

 that enable such larvae to breathe afford one of the most 



