8 
idly, and have been known to produce imagos before the close 
of the same season. Jvramea also seems to be two-brooded, 
emerging numerously both in spring and fall. On the other 
hand, the nymphs of the Gomphide probably require more 
than a year in which to mature, emerging in the second or 
third season after hatching. The one-year life cycle is, how- 
ever, the rule among the Libellulidw, which contains most of 
our commoner Anisoptera, the eggs laid during midsummer 
hatching in latesummer,and thenymphs maturing in time forthe 
general emergence the following season. In late August there 
is asurprising number of very small nymphs,—tiny spider-lke 
youngsters,—and even in September and October the prepon- 
derance of young nymphs is still manifest. As the period of 
maximum emergence of their species approaches, usually in early 
summer, they mostly attain full size, and are at this time most 
readily seen and captured and apparently more abundant than 
in the fall, when they were small and easily overlooked. With 
regard to the Zygoptera, it is highly probable that there are a 
number of broods ina season, the processes of transformation and 
oviposition beginning as soon as the weather permits and con- 
tinuing industriously to the close of the season. 
In the species whose life cycle is apparently more than a 
year the nymphs are of two or three distinct sizes, the largest 
presumably being of the next brood to emerge. In species 
whose life cycle is completed within a year, the nymphs are 
fairly uniform in size, but there is, nevertheless, a sufficient 
extent of variation to cause a considerable number of strag- 
gling emergences during the season; and it therefore follows 
that, in general, nymphs of nearly all species of Odonata may 
be found throughout the entire season. Because of this fact it 
has not seemed worth while to give dates of the occurrence of 
nymphs. The accessible data concerning the imago period, on 
the other hand, is very fully given, thus indicating the limits 
of the nymphal period also. 
Like many other immature aquatic forms, the ground color 
of the nymphs darkens greatly up to the close of each molting 
