NATURAL HISTORY WORK IN CART AGO 



6l 



extent, independent of each other, so that a given stage in 

 the blackening of the abdomen is not necessarily correlated 

 with a certain stage in the blackening of the thorax or of the 

 head. In other words, these changes appear at different 

 times in different parts of the same individual and in differ- 

 ent order in dilfferent individuals, just as changes in the 

 color of the hair of different parts of the human body, or of 

 different parts of the human head, take place at different 

 rates in different persons or even in the same person. 



The females of A. allopterum become pruinose on a slightly 

 more extensive area of the body than do the males and 



Right wings of the dragonfly Anisagrion allopterum, male. Enlarged 4 times. 



this pruinosity appears at an earlier stage in the blacken- 

 ing of the abdomen than in the other sex, but on the other 

 hand the blackening of the thorax and of the head takes 

 place relatively later. 



In all stages of its winged existence, whatever be its colors, 

 the male of Anisagrion allopterum is easily recognized by a 

 peculiarity of its hind wings which is not to be found in any 

 other dragonfly of Costa Rica. The vein which parallels 

 the front edge of the hind wing near its tip, when it reaches 

 the stigma is distinctly bent away from the front edge and 

 towards the hind edge, but continues to the wing-tip. For 

 some little distance outward from the point where the bend 

 occurs, this vein is markedly thickened and at the wing-tip 



