has a number of characters in common with the preced- 

 ing, and the two constitute the suborder Zygoptera. In 

 forms related to Calopferyx the three tracheated caudal setge of 

 the May-flies seem to be represented by three shorter and 

 thicker respiratory appendages, the laterals especially being 

 more or less spike-like and triquetral. In the Agrionidxe these 

 appendages are vertically flattened thin gill-plates. Quite a 

 different development of the original type is found in the 

 nymphs of the ordinary dragon-flies, the suborder Anisoptera. 

 In these respiration is principally performed by internal rectal 

 gills, and the three appendages, very short and subtriangular, 

 are supplemented by two others, the five converging to protect 

 the opening of the respiratory cavity. 



The five families constituting the Anisoptera — Petaluridce, 

 ^Eschnidre, GoniphUhe, Cordulegasten'da', and LihelUdidie — are 

 variously connected by common characters. It is worth not- 

 ing that the obscure color, rough sculpture, and general habits 

 of the Calopfei-i/x nymph are also found in the more primitive 

 forms of these families. The Petalur'uhf^ is probably the 

 oldest of the five. It has not as yet been found in Illinois. 

 In this family and the ^schnidfc the ovipositor is well devel- 

 oped and oviposition is endophytic, as in all the Zi/gojyfera. 

 The Petal It ridce, judging from Mr. Williamson's observations 

 (Williamson, '01), breed in boggy or swampy spots, where 

 the imagos may be found ovipositing. The nymph is re- 

 markably synthetic in its characters and supplies a hitherto 

 missing link in the evolution of the labium, being interme- 

 diate in this respect between jEschnidw and Cordulegaster- 

 idre, thus indicating a very primitive origin. In its form and 

 antennal structure, on the other hand, it strongly approaches 

 the GowpJiidm. In general, however, it is clearly most closely 

 related to the ^PJsrJinidce. The nymphs of the ^Eschnida' 

 are somewhat elongate, and climb on submerged branches, 

 driftwood, roots, and smaller vegetation. The imagos are 

 unusually large and high-flying, the eyes large, the wings 

 much specialized. The nymphs of the third family, Gom- 



