413 



places Calopteryx, and the family name Calopterygidae must be abol- 

 ished. The change has caused much confusion because of the former 

 application of the name Agrionidae ; but it seems practically certain that 

 further change would only result in still greater confusion, and the 

 family names as used by Muttkowski are, therefore, adopted without 

 change. 



The use of the common names "dragon-fly" and "damsel-fly" in 

 referring to the Anisoptera and Zygoptera respectively, causes no little 

 confusion because of the frequent use of the term dragon-fly to denote 

 the order as a whole. In the following pages, the words Anisoptera 

 and Zygoptera will be used exclusively to designate the subdivisions 

 of the order. 



ACKNOWLEDGMENTS 



I take pleasure at this point in expressing thanks for the valuable 

 aid which Dr. A. D. MacGillivray has given by his careful supervision 

 of work and thoughtful criticism during the course of the study. 

 Thanks are also due to Dr. S. A. Forbes for granting financial support 

 from the funds of the Illinois State Laboratory of Natural History 

 as well as for the loan of the collection of Zygoptera belonging to that 

 laboratory. I am especially indebted to Mr. E. B. Williamson for his 

 kindness in permitting me to examine his collection of Odonata ; and 

 I further wish to thank Dr. E. M. Walker and Dr. J. G. Needham 

 for the loan of specimens of zygopterous nymphs, and Dr. P. P. Cal- 

 vert for the identification of material sent him. 



Morphology 



NYMPH 



The nymphs are distinguishable from all other insects by the 

 possession of three more or less flattened, caudal, tracheal gills. They 

 are slender, delicate insects of the same color as the surrounding veg- 

 etation or environment in which they live and at first sight seem 

 hardly capable of the predatory habits of the order. They are usually 

 covered with fine hairs or spinules which collect an ambuscade of dirt 

 and rubbish. Their slender cylindrical abdomens resemble the stems 

 of plants and weeds, and the caudal gills remind one frequently of 

 growths of algae. Such adaptations as these render the insect most 

 inconspicuous in its natural habitat. 



Head. — The head of the nymph is somewhat oval or pentagonal 

 in outline when viewed from above, and is usually longer than wide. 

 The sutures are indistinct even in full-grown nymphs with the excep- 



