274 Annals Entomological Society of America [Vol. V, 
The insects were collected in the vicinity of Ann Arbor, Michi- 
gan, from various ponds, lakes, and marshy ground along the 
margins of streams. The Three Sister Lakes formed an excel- 
lent environment for collecting the nymphs. A large number 
of the organisms were taken in a pool, directly below the mill- 
dam, formed by the overflow of the Huron River, at Ann Arbor. 
METHODS. 
The experiments were performed in a dark room kept at a 
temperature of about 22°C. The intense artificial light was 
from the electric arc of a Thomson projection lantern. For 
the weaker artificial light, a 16 c. p. electric incandescent light was 
used. Experiments were also performed with diffused daylight, 
its source being a south window 5m. distant from the dark 
room. The light entered through a small circular opening in 
the side of the dark room. The nymphs were placed in a glass 
trough with parallel sides which was half filled with tap-water. 
The trough was then placed on a table top, painted black. The 
table was so situated that the glass vessel lay in the beam of 
light, entering through the circular opening, with its long axis 
practically parallel with the rays of light. 
RESPONSES IN NATURAL HABITAT. 
In their natural habitat, Agrionid nymphs react strongly to 
contact. They are found clinging tightly to the stems, branches, 
and leaves of Elodea and Ceratophyllum. This is an indication 
of their decided thigmotactic proclivities. They tend to place 
as much as possible of the external parts of their bodies in con- 
tact with a solid surface. This is accomplished by clinging to 
the aquatic plants, in such a manner that the long axes of their 
bodies lie parallel to the long axes of the stems and the branches. 
The nymphs frequently assume a somewhat different position, 
with the long axes of their bodies rather oblique to the long 
axes of the stems and branches. The creatures are frequently 
found with their bodies closely applied to the Elodea and 
Ceratophyllum at the points where the branches are given off— 
that is, in the forks formed by the stem of the main plant and 
the lateral branches. They are also found on both plants in 
the angles formed by the whorls of leaves arranged around the 
stem. Pearl (1903, pp. 560-562) records similar observations 
in his work on Planarians. This writer has given the name 
