62 IOWA STUDIES IN NATURAL HISTORY 
approach of the glass rod to the head essentially in the same 
manner, though not with equal promptness and precision. 
Neither could this response be elicited when the animals were 
reacting to other stimuli. 
Further experiments were made in an attempt to discover 
whether similar responses could be elicited by bringing the glass 
rod into proximity with other parts of the body. The majority 
of these experiments resulted negatively. However, several of 
the larvae sometimes reacted in a very definite manner when the 
glass rod approached the lateral surface of the anterior portion 
of the trunk. The initial response consisted in the contraction 
of the segmental muscles of the trunk on the side stimulated, 
which resulted in an appreciable curvature of the body. Fol- 
lowing this the animal would swim slowly forward. The re- 
sponse could not be elicited except when the animal was re- 
latively undisturbed by other stimuli. Neither was it entirely 
constant under these conditions. The area just posterior to the 
base of the gills proved to be the most sensitive area of the 
trunk. When the response was elicited by the near approach of 
the glass rod to this area not only did the characteristic con- 
traction of the segmental muscles take place, but the gills were 
also adducted. All attempts to elicit a response to the near ap- 
proach of the glass rod to the tail resulted negatively. 
The glass rod used in the above experiments was 4 mm. in 
diameter and rounded at the end. Clean glass tubes of smaller 
diameter were used with essentially the same results. When a 
galvanized steel wire 2 mm. in diameter was used the animals 
responded somewhat more vigorously than when the glass rod 
was used. Apparently the galvanized wire afforded a somewhat 
stronger stimulus than the glass rod. Other objects used as 
stimulating agents were a dissecting needle, a fine steel wire, a 
bone needle holder 6 mm. in diameter, rods of pine wood 6 mm. 
or less in diameter, and pieces of soft rubber tubing. The ani- 
mals responded to the near approach of all these objects es- 
sentially in the same manner, but somewhat less vigorously to 
the bone, wood, and rubber objects than to the glass rod. 
Five of the de-eyed larvae used in the initial experiments were 
kept in the laboratory and subjected to further experimenta- 
tion at irregular intervals. Whenever the experiments were 
