——— = 
== 


2. THE ADULT DRAGONFLY 
OR the beginner there is no difficulty about recognizing the 
two principal groups of dragonflies that make up the insect 
' order Odonata. These are 
Dragonflies proper: Suborder Anisoptera 
Damselflies: Suborder Zygoptera 
These are easily distinguished. The Anisoptera are stout bodied and 
have the hind wings broader at the base than the fore wings. The 
Zygoptera are slender and have fore and hind wings similar in form. 
When at rest the dragonflies hold their wings extended horizontally; 
the damselflies hold them laid together above the back, or at least 
(in Lestes) lifted obliquely.upward. In their immature stages, also, 
the two groups are equally easy to distinguish as will be seen in the 
next chapter. We will first discuss some of the characters they all 
have in common, and then proceed to the consideration of their 
differences. 
STRUCTURES 
Body Plan.—The body of a dragonfly is built upon the common 
insect plan, and its external, armor-like skeleton is composed of the 
same plates as in other insects. These parts are named in the accom- 
panying diagrams. The most peculiar features of its organization are 
(1) The head, largely overspread by the enormous compound eyes, and 
freely movable upon a neck-like projection of the thorax as on a pivot. 
(2) The large syn-thorax (fused meso- and metathorax), with side 
plates greatly elongated, slanted forward below and backward above. 
(3) The wings, of aeroplane aspect, strongly and peculiarly veined and 
highly efficient. (4) The legs, set well forward and adapted for perch- 
ing, and not for walking. And (5) The long abdomen, with accessory 
genitalia in the male developed on the under side of its basal segments. 
The head has for its framework a strong chitinous capsule, which 
is hollowed in the rear for the insertion of the neck, bulged at the front 
for the bench-like protuberance of the face, and expanded at the sides 
where covered by the huge eyes. It bears three ocelli and a pair of 
slender bristle-like antennae in front and the usual mouth parts 
beneath. Of these the upper and lower lips (labrum and labium 
respectively) are exposed to view, and only these will be further noticed 
in the descriptions of this book. The two pairs of included jaws 
(mandibles and mazillae) which show only their toothed tips between 
11 
