392 the canadian entomologist 



Mutual Adaptation of the Sexes. 



I have noted elsewhere* that in Aeshna constricta and its alHes 

 the abdominal appendages of the male are specialized for a firmer 

 grasp of the head and prothorax of the female than in those species 

 in which these structures have their usual form, and that these 

 modifications are probably correlated with the more erratic nuptial 

 flight of the species of this group. In StauropJilehia the general 

 form of the male superior appendages recalls that of Aeshna con- 

 stricta, but is still more highly specialized, having in addition to a 

 very prominent subapical denticulate crest formed by the extreme 

 elevation of the distal part of the superior carina, and the bending 

 upwards of the margin at its termination, a process from the dorsal 

 surface and supero-external margin, just before the middle, directed 

 horizontally inwards and slightly decurved at apex(pl.XVII.,fig.lA). 

 The inferior appendage is also complicated by the presence of a 

 prominent elevation rising almost perpendicularly from the superior 

 surface of the appendage at its extreme base (fig. 1, b. inf.). 



The appearance of these appendages suggests a very firm union 

 between the two sexes during copulation, and it is therefore of 

 interest to learn from Mr. Williamson's notes that the nuptial flight 

 is very erratic. 



I relaxed the separated abdomen of a male and the head and 

 thorax of a female, and endeavoured to determine the exact nature 

 of this union. This was an easy matter as far as the head of the 

 female was concerned, but with regard to the prothorax, much 

 careful manipulation was necessary. I think, however, the follow- 

 ing account will prove substantially correct. 



By applying the upper surface of the inferior appendage to 

 the front of the head in the usual position for the Aeshninae the 

 basal elevation was found to fit accurately in a depression on the 

 rear surface of the female's head just below the occipital margin 

 (fig. 1, b. inf.). This feature alone must, render the grasp of the 

 male firmer than in those species which lack the prominence. The 

 superior appendages also fell naturally into position at the rear of 

 the head on the slope of the concavity surrounding the occipital 

 foramen, from which their inner margins were but narrowly 



'1912, Walker, E. M., Univ. Tor. Stud., Biol. Saries 11, pp. 3S-42. 



