[VoL XXXII. 
might be enlarged, should necessity arise for the entrance of 
air from a new quarter. Following this, the atrophy of the old 
connection would complete the switching; which, we believe, 
is what has happened in the Zygoptera. It follows from this 
that, so far as this portion of the wing is concerned, the Zygop- 
tera depart more widely from the primitive type than do the 
Anisoptera. From this brief sketch it is evident that these 
parts will furnish systematic characters which are as yet unused. 
For increasing its efficiency, certain methods of bracing the 
dragon-fly wing in its costal and basal parts have been per- 
fected to a degree surpassing anything to be seen in any other 
order. The veins of the costal margin are thickened and 
approximated as usual ; but the strong corrugation of the area 
traversed by them is maintained by their being bound together 
908 THE AMERICAN NATURALIST. 
an I 
L \ 7 CU, 
4°32" Cu, 
Fic. 65.— ram setting forth the behavior 
are stages in the 
scent of the mit cross-vein which are to 
be seen in such living gen as Tetra 
themis, Anatya, Liheltule: ead aie 
ectively. 1', 2', 3’, and 
2 as seen in the 
fore wings of tone gory Aratya raya 
lula, and Tetragoneuria. 1”, 2", 3" 
na, 
Mesothemis, Anatya, and Nannodythemis. 
at the nodus, at the stigma, and 
often toward the base, where 
certain of the antenodal cross- 
veins become greatly thickened. 
These hypertrophied antenodals 
sometimes (as in Æschna) be- 
come stout triangular trusses 
which completely fill, in section, 
_ the furrow between the costa 
and the radius. Toward its base, 
the wing is braced by two char- 
acteristic structures well known 
in the literature of the Odonata 
e 
as the arculus and the triangle. 
The arculus has already been 
discussed.} 
The Triangle. — The deflection 
of the cubital trachea, just before 
its fork, makes a place for the de- 
velopment of the triangle. This 
is one of the most important 
features of the wings in the suborder Anisoptera, to which 
alone the following remarks will apply. 
While its stout bound- 
1 American Naturalist, vol. xxxii, No. 376, p. 234, Fig. 7- 
