422 MORPHOLOGY OF THE ABDOMEN IN THE ODONATA 



also contains two pairs of inferior tergals as in the preceding 

 segment. 



In the females the eighth and ninth segments have a pair of 

 muscles not necessary in the males : the Transverse Genitals of 

 the eighth segment (tsg-8). 



III. Anisoptera. Libellulinae 



Specimens of several species {Lihellula pulchella, Plathemis 

 lydia, Erythemis simplicicollis, Periihemis domilia, and Tramea 

 Carolina) were dissected. Many of these are figured below and 

 the comparisons between these genera can best be made by a 

 study of the figures. In essential details they are almost alike, 

 and also very similar to the Aeshnids. No attempt will be made 

 to describe them. A few contrasts may, however, be pointed 

 out. 



With the shortening and widening of the body the internal 

 organs change in proportion. The nerve ganglia are rounder, 

 the connectives heavier and farther apart; the alimentary canal 

 has a greater diameter but its parts are located as usual; the 

 reproductive organs are the same except perhaps for more direct 

 oviducts and vasa deferentia; and the muscles are wider and 

 flatter. 



Figures 37 and 38 of Tramea Carolina were drawn from an 

 advanced teneral specimen which had not as yet taken food. 

 The distended crop and ventriculus will be noted. They are 

 filled with gas, in all probability air. The same figure also 

 shows the immature condition of the ovaries, scarcely more ad- 

 vanced than those of the larva. The nymphs of the Zygoptera, 

 especialty, have much more mature gonads than these seem to be. 



SUMMARY OF COMPARATIVE MORPHOLOGY 



A comparison of the anatomy of the systems studied in these 

 three important groups of Odonata shows clearly the fact that 

 the larva and the imago have in each case followed distinct and 

 different lines of specialization. In successively higher groups 

 the structures of the larva become more intricately adapted for 

 aquatic existence, while in the imagoes the two higher groups 

 are very much better fitted for flight and aerial existence than 

 are the Zygoptera. 



