318 STEPHEN G. RICH 



studied in a few isolated forms. The present study is intended 

 to cover this field comparatively. Twenty-one genera, compris- 

 ing all save the most .rare ones of the Cayuga fauna, have been 

 studied. The work was undertaken at the suggestion of Dr. 

 J, G. Needham, to whom I am much indebted for material and 

 for critical advice. Through him I was able to see the un- 

 published work of Miss Andrews, to which I refer often. Dr. 

 Philip P. Calvert, of Philadelphia, allowed me the use of some 

 sections of Calopteryii and a stained and mounted rectum of 

 Cora chirripa. Dr. W. A. Riley and Dr. Needham loaned me 

 sections of Libellula, and Mr. E. A. Richmond, of Cornell Uni- 

 versity, provided some excellent Corduline material from New 

 England. 



MATERIAL AND METHODS 



The greater part of the work here described was done by dis- 

 section under the binocular microscope. The higher powers of 

 the prismatic binocular were ample for all work save the details 

 of tracheation. The dissections were supplemented by sections 

 in a few cases, notably in Calopteryx and Libellula. 



Fresh material was, in the main, the most satisfactory, but 

 that which had been preserved in 2 per cent formalin was in 

 most cases almost as good. In it fat stood out better and 

 tracheation was not lost. Alcoholic material was usually in 

 bad shape, being badly contracted and having only the larger 

 branches of the tracheae visible. 



HISTORICAL REVIEW 



According to Hagen ('52) the nymphs of Anisoptera were pos- 

 sibly first observed by Aristotle, under the name of 'Orsodacna.' 

 Charlton (1671), Rondelet (1555), and Swammerdam (1686) were 

 the first among the moderns to observe and describe the nymphs. 

 Rondelet calls them 'water cicadas.' The first recognition of 

 their larval character was by Swammerdam. Poupart (1702) 

 was, without doubt, the first to see the anisopteran nymphs take 

 water into their rectum, and Reaumur (1742), repeating the 

 observation of Poupart, also noticed the enlarged branchial 

 rectum, as did Roesel in 1744. 



