4 G. H. PARKER 



in schools and not individually, A single fish in an aquarium 

 rarely finds hidden food for the reason that it remains most of the 

 time quietly at the bottom, a position of protection that is assumed 

 by a school of Fundulus when disturbed. If, however, there are 

 a number of fish in the aquarium, they soon rise to the higher 

 water, play about, and thus have a much better chance to run 

 across traces of food. For this reason, I have generally not ex- 

 perimented with single fish, but with small groups of at least five 

 or six. 



The part played by the olfactory organs in reactions to hidden 

 food can be determined by first eliminating these organs and then 

 testing the fishes. The olfactory apparatus can be rendered in- 

 operative by cutting the olfactory tracts in a position where they 

 are easily accessible as, for instance, between the eyes. In this 

 situation a small incision can be made through the thin bony roof 

 of the skull and the two tracts can be cut by a single movement 

 of a narrow blade. The first operations of this kind that I carried 

 out were done under ether, but subsequent tests on normal fishes 

 showed that etherization of itself, i.e. without any operation, left the 

 fishes in such a condition that they could not distinguish for a 

 number of days packets of cloth without inclosed meat from those 

 that included meat, and, therefore, I was driven to carry out these 

 operations without the use of an anesthetic. Twenty-four hours 

 after such an operation, the fish were fully active, took food, and 

 in all obvious ways seemed normal. When two packets of cloth 

 one with dogfish meat hidden in it and the other without this food, 

 were suspended in the aquarium in which the operated fishes 

 were, these animals nibbled temporarily both packets in a way 

 that made it impossible for an uninformed observer to dis- 

 tinguish one packet from the other. When these two packets 

 were transferred to an aquarium of normal fish, the one containing 

 the food was soon surrounded by a vigorously contesting assembly 

 of fishes, whereas the packet without food was only occasionally 

 nibbled. The evidence from these experiments favors the view 

 that the olfactory organs are necessary to Fundulus in sensing 

 hidden food. The severity of the operations, however, makes this 

 evidence not wholly conclusive. 



