80 PRELIMINARY NOTES ON THE ODONATA. 
like a mask over the face. The wings are represented by wing-pads 
which enlarge as the successive moults occur. The more external 
organs of respiration differ in the two sub-orders, the damsel-flies 
breathing by means of three terminal caudal gills and the dragon-flies 
by drawing water into a highly modified rectal chamber, exchanging 
gases and again pushing the water out. 
The nymphal stages last in different forms from two to four or 
five years. In Eeshna Walker’s observations indicate that about a 
dozen moults are accomplished. At each of these periods changes in 
form and the development of systems can be noted. During the months 
or years thus occupied the nymphs spend their time in capturing food, 
some searching the debris at the bottom, some burrowing in the mud 
or sand and others climbing amongst the submerged vegetation. 
For a week or two before the last moult, which is to end its aquatic 
existence, it is quiescent and eats little or nothing. Internal changes 
are occurring with great rapidity and certain of them can even be 
seen from the exterior, as the withdrawal of the adult labium from 
that of the nymph. When reorganization is completed the nymph 
crawls out of the water and clings to some support until its cuticle drys 
and splits across the head and down the back of the thorax. Within 
ten to twenty minutes the head, thorax, legs and wings may be free 
from the larval shell. At this stage there is usually a rest of several 
minutes, followed by the freeing of the abdomen as the imago clings 
to the shell or exuvia it is abandoning. All parts of the body are now 
extended or expanded to their proper adult proportions, the wings 
changing most remarkably, and the process of hardening or chitinizing 
the cuticle begins. If weather conditions are favorable and no calam- 
ity in the form of bird, frog, fish or larger dragon-fly appears, the 
imago may be ready for flight in a few hours; the colors do not mature 
completely for some days, however, and the reproductive system 
requires a still longer time for development. 
Thus the day of feeding is not past, as is practically the case 
with many other insects, and they spend their time for a month, more 
or less, in devouring the Diptera and small insects about the pond or 
stream from which they recently emerged or over neighboring pas- 
tures or roadsides. 
When sexual maturity is attained pairing and ovipositing become 
the paramount issues. There seems to be little if any courtship in the 
Odonata, and struggles between males for the possession of the female 
are rare. There are, however, apparent exceptions to the latter state- 
ment: Kellicott believed that Caloptery~ and Hetaerina generally 
