62 A YEAR OF COSTA RICAN NATURAL HISTORY 



the cells (or small areas bounded by veins) are distinctly 

 smaller than they are in the corresponding part of the fore 

 wing. In the older males these small cells become partly or 

 completely filled by thickening of chitin (of which the veins 

 are chiefly formed) and in this condition strongly suggest 

 the condition to be found in any dragonfly's wing which has 

 been injured before, or at, the time of transformation. 

 Twenty-five years ago, this peculiarity of allopterum males 

 might have been seized upon as an example of an inheri- 

 tance of mutilation effects, but it can hardly be regarded as 

 such now. Insignificant as these structural details of the 

 wing of this little insect may seem, they are very constant. 

 Indeed the arrangement of the veins of the wings of these 

 and many other insects is among the most reliable of recog- 

 nition marks, and the trained entomologist can often identify 

 an insect from a detached wing or even, in some cases, a 

 wing-fragment, with perfect certainty. Finally be it added 

 that the hind wing of the female of allopterum shows only a 

 slight tendency toward these features of her partner. 



Still more abundant about Cartago, perhaps the most 

 abundant dragonfly of the vicinity, was Argia extranea, 

 about iVg inches long, Vs to 7^ of an inch longer than Jnis- 

 ngrion allopterum. The male is bright blue marked with 

 black; the female has the blue of the male replaced by a 

 pale brown or a violet brown. The genus Jrgia is very char- 

 acteristic of tropical America, where it is represented by 

 many species, some of them resplendent in metallic body 

 colors, and a few species reach even to Canada. It is dis- 

 tinguished, among other features, by the length of the stiff 

 hairs or bristles on the legs, which are twice, or more than 

 twice, as long as the intervals between them. Argia ex- 

 tranea lives throughout a large part of Costa Rica. Watch- 

 ing a female laying eggs in a plant at Juan Viiias on June 24, 

 1909, we brought a bit of the plant in water to Cartago and 



