428 MORPHOLOGY OF THE ABDOMEN IN THE ODONATA 



the gradual tapering of the anterior into the posterior ]wrtions of 

 the body, the development of rudder expansions laterally on the 

 posterior end of the body. All these not only remind one of, 

 but actually reproduce for him, the bodies of the Aeshninae and 

 Gomphinae. That length alone is not the only factor is easily 

 seen here and it is just as clearly illustrated in the Zygoptera 

 with their weak thorax, proportionately large wing surface, and 

 long slender abdomen with no basal enlargement. 



■2. Copulation and Ovipositio7i. A review of Calvert s sugges- 

 tion that the elongated abdomen of certain Pseudostigmatinae 

 is an adaptation to oviposition was given in the early part of this 

 paper. During the purely anatomical investigation following, 

 no light has appeared upon it. Some illustrations selected from 

 the table of comparative measurements (page 387), however, may 

 be of use. The genus Lestes is well represented there. So far 

 as the writer has observed all the species named have the same 

 general habit of oviposition — that of bvnying the eggs in the 

 tissues of plants growing in or near the water. As many as a 

 half dozen of these species have been taken on the same day 

 ovipositing in the same place and upon the same plants. It was 

 impossible to see that the longer bodied species, as L. redangu- 

 laris, vigilax, and eurrnus, possessed any advantage over the 

 shorter forms. None of them of course had the habits of Mecis- 

 togaster. 



But, granted that the longer forms did possess some advantage 

 in this line, why should the males of these species be so much 

 longer than the females? They could scarcely find a special use 

 for so long an abdomen even though they did accompany the 

 female, grasping her as many do, during oviposition. Dr. Cal- 

 vert suggests that the male must be elongate if the female is 

 so to meet the necessities of copulation, but he gives no explana- 

 tion for a male having a length of 42 mm. when the female is 

 but 32 mm. as in the case of L. rectangular is. It seems very 

 probable that Mecistogaster uses her long abdomen to advantage 

 in the way suggested, but that does not mean that the elongated 

 abdomen is an adaptive variation. 



In cases where the male accompanies and holds the female as 

 she lays her eggs the expectation would be that the male abdomen 



