20 DRAGONFLIES OF NORTH AMERICA 
and is not an appendage of the vesicle of the third segment: it stands 
in the place of the penis sheath of the Anisoptera. 
Such of these parts as are used in diagnosis of species in this book 
are illustrated in figure 8. 
In all Zygoptera and in many Anisoptera there is an ovipositor 
developed at the genital opening of the female; and when this is 
developed, the anterior lamina of the male is cleft to accommodate 
it in copulation. Females that possess an ovipositor make punctures 
with it for the reception of their eggs, either in green stems, or in logs 
or bottom mud. 
At the front of the mesothorax in the females of the bluets and other 
small damselflies there is a pair of minute plates that are much used 
in the determination of species. These rise beside the mesothoracic 
spiracle or stigma and are called mesostigmal plates. They are over- 
lapped more or less by the hind lobe of the prothorax and are so 
minute that a lens is required for their examination. On the front of 
the synthorax is a conspicuous Y-shaped ridge. The stem of the Y is 
the carina; the fork above, beside the wing roots, is the crest; the trans- 
verse ridge at the front next the prothorax is the collar; and on either 
side at the junction of the carina with the collar lie the mesostigmal 
plates. They are figured for many of the species of the larger genera 
of Coenagrioninae in the following pages. 
