78 PRELIMINARY NOTES ON THE ODONATA. 
Fie. 13. Anax junius assuming defensive attitude. Dragon flies, however, 
do not sting. Photo by A. D. Wheden. 
Again Professor Needham’s work in Illinois and New York 
upon the life histories and the nymphs of the dragon-flies has stimu- 
lated new interest in a neglected phase of the work on this order, most 
of the papers having dealt with the adults only. Among the many 
who have since added to the results of Calvert and Needham none has 
done more than Dr. Walker during his study of Canadian species and 
in his revision of the genus Aeshna. 
To aid us in clearing up the whole history of the group have 
come several European writers on fossil insects, Handlirsch in the 
lead, with descriptions, illustrations and classifications of fossil 
Odonata. In America Professor Cockerell has unearthed several very 
interesting forms which have been carefully studied by Dr. Calvert. 
Professor Needham also made very considerable use of accessible 
Odonate fossils in his paper on wing venation. 
Thus, from a biological point of view at least, the progress made 
during the past score of years in our knowledge of American dragon- 
flies is of significance. On the one hand general principles have been 
