NO. 1571. DRAGONFLIES OF BURMA AND SIAM— WILLIAMSON. 269 



similar in form. Calopteryginae generally do not display great 

 sensitiveness to weather conditions. Temporary cloudiness and slight 

 changes in wind or temperature do not result in immediate decrease 

 of activity or in search for a new environment. There is reason to 

 helieve that as a group the species have a moderately long or pro- 

 tracted seasonal range. 



Comparing now the subfamily Gomphinae — the largest of the 

 subfamilies considered in this paper — with the Calopteryginsp, I 

 find in the former only slight differences, if any, between the sexes 

 of anj^ species, and these almost entireh^ confined to body-mark- 

 ings. Moreover, the GomphinsB are as a group obscurely or pro- 

 tectively colored. ISIetallic or other brilliant colors, so common in 

 CalopteryginiP and in certain beetles which are not eaten by birds 

 are unknown. The ground-color varies from pale brown through 

 various shades of brown and yellowish or reddish brown to black. 

 The markings are from Avhite through pale green, green, pale yellow, 

 and clear yellow to orange; or the ground-color may be the paler, 

 marked w4th the darker colors. The A\4ngs are hyaline, or slightly 

 fumose. In wing venation these dragonflies are highly specialized, 

 adapting them to protracted flights. For example, some species 

 spend much of their time in tall forest trees and during a day may 

 make numerous trips from a stream to trees at considerable dis- 

 tances from the water. There is reason to believe that certain 

 species spend much of their lives at a distance from the streams 

 which gave them birth, being fully able, when the time arrives, to 

 return by rapid and sustained flight. The size, stnicture, and con- 

 sistency of these insects make them favorable food for medium- 

 sized or larger insectivorous birds, and it \\\&j be well supposed that 

 natural selection has tended to suppress brilliant colors and habits 

 which would attract attention. The males do not make themselves 

 conspicuous by pugnacious attacks on each other. Several may 

 be on the wing in close proximity without attacking, though they 

 fre(}uently approach as if in search of females. In the form of the 

 abdominal appendages of the male the Gompliinae are highly special- 

 ized. In the oriental region Onychogomphus is represented by the 

 greatest number of species, and in this genus both venation and 

 male appendages are highly specialized. This specialization and 

 presumably more perfect adaptation of the appendages to their 

 use would render the speedy capture of the female almost certain. 

 Moreover, the scattering of the species through woodland and fields 

 adjacent to streams woukl render the meeting of individuals to 

 some extent accidental. In view of these facts conflicts between 

 males are probably the exception. During the act of copulation 

 Gomphinse generally seek more retired and elevated places than 

 the Calopteryginae. Some Gomphiiii^, at least, displaj^ great sen- 

 sitiveness to weather conditions, appearing about certain favorite 



