

IV] THE LARVA OR NYMPH 97 



When the larva has selected its position for transformation, it 

 fixes its tarsal claws so firmly in position that the exuviae remain 

 clinging tightly to their support long after the imago has emerged. 

 The larva then becomes quite motionless, while the internal swelling 

 of parts increases (B). This swelling becomes particularly pro- 

 nounced in the region of the eyes, and on the back of the thorax. 

 The actual splitting of the skin first appears along the mid-dorsal 

 line of the thorax, and quickly extends forward on to the head. 

 It seems to be caused by the insect arching its back strongly, in an 

 attempt to withdraw its head into the thoracic cavity. The 

 thorax bulges out through the crack, so that the withdrawal of 

 the head is quickly accomplished. As soon as head and thorax 

 are free, the legs and wings are gradually withdrawn from their 

 sheaths (c). By the time this is accomplished, the abdomen is 

 only partly free. The insect next usually hangs for some time 

 with its head downwards, while the action of sun and air hardens 

 its legs (D). As soon as these are strong enough, the insect waves 

 them about in an effort to find something to catch hold of. Nothing 

 being usually available, it attempts to jerk itself upwards, and 

 sooner or later succeeds, by a great effort, in seizing the head of 

 the exuviae, or the reed-stem above it (E). Next, holding firmly 

 on to the stem, the insect withdraws its abdomen from the larval 

 skin, and usually climbs a little way above it, so as to be quite 

 free. The Gomphinae crawl straight out of their skins, often with 

 barely any rest for the drying of the legs. 



The transformation is completed by the elongation of the 

 abdomen and the expansion of the wings (F, G). The abdomen 

 is usually broad, short, and very soft when first withdrawn. In 

 Petalura and in most Aeschninae, it is already a considerable 

 length, and reaches its full extent before the wings have completed 

 their growth. In other forms, the abdomen usually completes its 

 lengthening after the wings are fully expanded. The process is, 

 however, always correlated with the growth of the wings. There 



o o 



seems to be no doubt that the mechanism of expansion is a com- 

 bination of a rapid pulsation of the blood with the swallowing 

 of a large amount of air into the alimentary canal, and, 

 particularly, into the crop. Thus, not only is the abdomen 

 considerably expanded, but blood is displaced by air within it, 



T. D -F. 7 



