ZOOLOGY, ENTOMOLOGY, AND MEDICINE 235 



VARIATION IN THE GILLS OF ZYGOPTERA* 

 Philip Garman, University of Illinois 



The gills of the nymphs of Zygoptera show features which 

 serve as accurate indices to specific and generic relationships 

 within the suborder. The separation of closely allied species 

 is frequently accomplished with ease by observing the outline 

 of the gill, pigmentation, tracheation and so on. This feature 

 should probably take precedence over the characters of the 

 labium which cease to be of great importance in groups of less 

 than family size. 



The groups showing the more marked variations in gill 

 structure are found with the Coenagrionidae, but there are 

 also variations in the gills of Lestinae which serve to distin- 

 guish the different species. In the genera of Coenagrionidae 

 the species grouped by means of gill structure conform re- 

 markably to the groups of species, or superspecies, as based on 

 adult characteristics. This feature is evident to a greater de- 

 gree in Enallagma, and the groups based on both nymphal 

 and adult characters are seen below : 



BASED ON ADULT STRUCTURE BASED ON NYMPHAL GILLS 



Enallagma civile. Enallagma civile. 



Enallagma carunculatum. Enallagma carunculatum. 



Enallagma calverti. Enallagma calverti. 



Enallagma hageni. Enallagma hageni. 



Enallagma geminatum Enallagma geminatum 



Enallagma exsulans. Enallagma exsulans. 



Enallagma antennatum. Enallagma antennatum. 



Enallagma traviatum. Enallagma traviatum. 



Enallagma signatum. Enallagma signatum. 



Enallagma pollutum. Enallagma pollutum. 



"Based on data now being published in a bulletin of the Illinois State Labor- 

 atory of Natural History. 



