3o6 Papers from the Marine Biological Laboratory at Tortugas. 



siderable power of discrimination. The atherinas and cassiupca pieces were 

 much ahke. They were identical in color, but differed in details of form and 

 in translucence, as well as in palatability. In spite of their likeness the snap- 

 pers discriminated accurately between them. That this discrimination was 

 based on form or translucence rather than on color appears from the fact 

 tliat the snappers were not deceived when red cassiopea was substituted for 

 blue, and from the further fact that they took at once the combined atherina- 

 cassiopea. It is clear that no conspicuous difference, no warning coloration, 

 was necessary to enable the snappers to rapidly differentiate the two sorts 

 of objects. 



Experiment J5. On July 23 two small aquarium jars of uncolored ather- 

 inas preserved in formalin wf-re fed to the laboratory colony of snappers. 

 No record was kept of the number fed, but it was estimated to be between 

 200 and 300 or 2 atherinas to each of the 150 snappers. The atherinas 

 were taken from the 2 per cent formalin, rinsed in sea-water, and thrown 

 at once, while still saturated with the formalin. They were all taken, but 

 very slowly toward the end. Soon snappers were frequently seen swim- 

 ming about with heads of atherinas projecting from their mouths; 15 min- 

 utes later many (probably 50 or 100) atherinas that had been disgorged by 

 the snappers could be seen on the bottom under the dock. 



On July 24 blue formalin atherinas were offered to this colony. They 

 were taken very slowly, and after 30 or 40 had been taken, they were re- 

 fused. Many were then disgorged. In the midst of this feeding of blue 

 atherinas some perfectly fresh uncolored individuals were oiifered. Some of 

 these still had enough life to wriggle feebly. These were cautiously ap- 

 proached by the snappers, which often jerked back from them, but finally 

 took them. The living fish, while still wriggling, were thus treated by the 

 snappers in a manner wholly unlike that usual to them when fed on fresh 

 atherinas. It was clear that the snappers had retained since the day before 

 an association between the atherinas colored or uncolored and the dis- 

 agreeable qualities of formalin. 



Atherinas are inconspicuous when seen against the surface film or the 

 sand bottom, as the snappers see them. They may be regarded as pro- 

 tectively colored. If all the atherinas about the island were suddenly to be- 

 come highly unpalatable, I do not doubt that the snappers would learn after 

 a brief experience to let them alone. I do not doubt that they would be 

 effectively protected by unpalatability alone, without the addition to it of a 

 warning coloration so rapid and so nice is the power of discrimination in 

 the gray snapper. This ability of the snapper to discriminate with nicety 

 has led to its adjustment to all the food elements of its environment. Frag- 

 ments of a large coral polyp which I threw to them were taken, but at once 

 rejected. Pieces of the arm of a brittle-star were examined and left un- 

 touched. Both were inconspicuous. A palinurus, 3 inches long, was at 



