ONTOGENY 39 
position 15 minutes, resting. Then it turned forward, fastened its feet, and 
withdrew its abdomen. Rested until wings were fully expanded; half an hour 
expanding its wings. Time from leaving water until wings were fully expanded 
(but not dry), one hour. Water was squirted on top of thorax three or four 
times at intervals of several minutes before the skin broke open.” 
The cast skins left behind at transformation are called exuviae. 
Though rent down the back and gaping they preserve perfectly the 
form of the nymph, and are very satisfactory material for the study 
of chitinous nymphal structures. Labia and other parts when de- 
tached, outspread and mounted, show skeletal structures most clearly. 
In all life history work the skins should therefore be carefully preserved 
and labelled to correspond with the individuals that come out of them. 
The exuvia are left at transformation somewhere near the edge of 
the water. The smaller damselflies clamber up the slender stems of 
emergent water weeds, usually about an inch above the water surface. 
The club-tail nymphs (Gomphinae), with legs set wide apart, require 
broad surfaces on which to ascend, such as trees or logs, or more often 
they transform while lying flat on the sand or mud within a few inches 
of the margin of the water. The belted skimmers (Macromiinae) go 
farthest afield to transform, often climbing up tree trunks and fences 
some meters distant from the shore. 
