Dragon-flies and Damsel-flies 
87 
cast nymphal skins or exuviae, clinging here and there to stones and plant- 
stems. Attached to these exuviae there may be often noted two or three short, 
white, thread-like processes. These 
are the dry chitinous inner linings 
of the main tracheal trunks of the 
dragon-fly which were moulted with 
the outer body-wall. As the main 
tracheal tubes are really invagina¬ 
tions of the outer skin, it is obvious 
that the inner lining of the trachea 
is continuous with the outer coat 
(chitinized cuticle) of the body-wall 
and so is naturally cast off with it. 
Although the habits of the adult 
dragon-flies must be studied out of 
doors, the nymphs can be brought 
indoors and kept alive so that their 
walking and swimming and hiding Fig. i 18.—Adult and last exuvia of the damsel- 
and capturing of prey, and often Ay, Lesles uncala. (Natural size.) 
their transformation into winged imagoes, can be readily observed. In 
their natural habitat some of these observations are nearly impossible, 
and for school-room or private-study aquaria 
hardly any other animals can be found of 
more interest to the observer, whether child or 
grown-up, than the dragon-fly nymphs. 
Professor Needham, who has done more 
and better work in the study of the immature 
life of dragon-flies than anybody else, gives 
the following directions for collecting and 
rearing the nymphs: 
“If one wishes to collect the nymphs which 
lie sprawling amid fallen trash, a garden-rake 
with which to draw the trash aside, fingers not 
too dainty to pick them up when they make 
themselves conspicuous by their active efforts 
to get back into the water, and a pail of 
water in which to carry them home, are all 
the apparatus required. 
“A rake will bring ashore those other 
nymphs which burrow shallowly under the 
sediment that lies on the bottom, and also a few of those that cling to vegeta¬ 
tion near the surface; but for getting these latter a net is better. Fig. 119 
Fig. i 19. —A home-made water- 
net for collecting dragon-fly 
nymphs. (After Needham.) 
