OBSERVATIONS ON THE ECOLOGY OF DRAGON-FLY 
NYMPHS: REACTIONS TO LIGHT AND CONTACT.* 
By C. F. Curtis RiILEy, 
CONTENTS. 
I. Introductory. 
II. Methods. 
III. Responses in Natural Habitat. 
VI. Enemies. 
VE Hood: 
VI. Response to Intense Artificial Light. 
VII. Movement Away from the Light Not a Response to Temperature. 
VIII. Response to Contact. 
IX. Formation of Groups. 
X. Inhibition of the Photic Response. 
XI. Change of Bodily States. 
XII. Disintegration of Groups. 
XIII. Indefiniteness and Change of Photic Response. 
XIV. Response to Less Intense Articfiial Light. 
XV. Response to Daylight. 
XVI. Summary and Conclusion. 
INTRODUCTORY. 
The greater part of this work was completed several years 
ago. Publication has been delayed through various causes; 
chiefly because it had been the purpose of the writer to incor- 
porate other experiments in the paper. The present communi- 
cation is really an abstract of a more detailed piece of research 
which is practically completed, except for certain minor matters. 
The research was undertaken at the suggestion of Professor 
©. J. Holmes. The writer desires at this point to express his 
appreciation of Doctor Holmes’s kindly criticisms and also of his 
stimulating interest in the work of those associated with him. 
Thanks are also due to Doctor C. C. Adams for free access 
to his library and for many helpful suggestions. 
The work was done upon certain forms of Agrionid nymphs. 
Many hundreds of different individuals were used in the 
experiments. It proved to be impracticable to identify the 
forms as the work progressed. A representative series of the 
nymphs were sent away for determination and, unfortunately, 
were lost in the mail. No essential differences have been found 
in the reactions of the different species, other than those of 
differences in degree, as evidenced in a few cases by relative 
inertness and activity. 
cs Contributions from the Zodlogical Laboratory of the University of Illinois, 
under the Direction of Henry B. Ward, No. 20. 
273 
