64 IOWA STUDIES IN NATURAL HISTORY 
is not without interest. Parker and Van Hausen (’17) de- 
seribed the responses of the catfish (Amiurus nebulosis) to me- 
tallic and non-metallic rods. The only non-metallic rod to the 
near approach of which these fishes responded when deprived 
of their sight in the experiments of Parker and Van Hausen, 
was a rod of cedar wood. This response, as suggested by these 
authors, was mediated through the sense of smell. Crozier 
(718) described the responses of the de-eyed hamlet (KH pine- 
phelus striatus) to the near approach of rods of various metals 
and woods as well as such miscellaneous substances as glass, 
hard and soft rubber, porcelain, hard paraffin, sandstone, and 
compressed carbon. 
According to Parker and Van Hausen the blindfolded eat- 
fishes usually responded to a metallic rod approaching them in 
the water by swimming away when it was still some centimeters 
distant. However, if but a small portion of the metal was in 
contact with the water they sometimes responded by moving to- 
ward the rod and even nibbling at it. According to Crozier, 
when a glass rod approaches the head of a de-eyed hamlet to 
within 4.5 or 5 em. ‘‘the fish bends in the opposite direction and 
swims slowly backward; or it may back deliberately away for 10 
or 15 em., then abruptly turn away from the side stimulated and 
assume a position at right angles to that held before being stimu- 
lated.’’ He noted also that when the rod approached the caudal 
peduncle the first response of the tail was to bend toward the 
opposite side. The initial reaction in these responses as in the 
characteristic responses of the catfishes to the near approach 
of a metallic rod is an avoiding reaction ; consequently it is nega- 
tive in character. On the other hand, the initial reaction in the 
typical response of the de-eyed larvae of Ambystoma tigrinum 
to the near approach of a solid body to the head is a movement 
toward that body; consequently, it is positive in character. Par- 
ker and Van Hausen have demonstrated conclusively that the 
responses of the blinded catfishes to the near approach of me- 
tallic rods in the experiments described by them were stimulated 
by electrical currents generated on the rods in contact with the 
water. They have shown also that a positive reaction, i. e., a 
movement toward the rod, occurs only when the stimulus is very 
weak. Inasmuch as the de-eyed hamlets in Crozier’s experi- 
