NATURAL HISTORY OF AMIA OALVA LINNAEUS. 63 



No. 8. The red-spot male. A bright red pigment-spot in front of and below 

 the eye on the left side. 



No. 9. The deep-split-tail male. Tail split as in No. 5, but the split was higher 

 and deeper. 



No. 10. The scarred male. A long, white scar back of the right narial 

 tube. 



In order to recognize the individual fish by such characters one must of course 

 be within four or five feet of it. Whether the individual pigment-marks persist 

 through the year was not made out; the accidental anatomical peculiarities are 

 probably transient. 



It is of interest to note that the color differences between the sexes, as well 

 as individual peculiarities of color and proportions, form the basis of the species 

 formerly recognized by systematists (see Dumeril's Key, '70, p. 417). 



In order to see whether the brighter light or the higher temperature to which 

 the male fishes are exposed in shallow water during the breeding season is the stim- 

 ulus inducing the color change, two males taken on the spawning ground in a net 

 on April 13, 1901, were placed on April 17, the one in an aquarium covered with 

 black cloth, the other in an aquarium uncovered and placed against a west window. 

 Both aquaria were provided with running water, and throughout the experiment 

 with light the temperature in the two aquaria remained the same, not varying 

 more than one degree from 15° C. 



The following notes were made on the colors. 



April 13. The two fish placed side by side were identical in coloring. Tail- 

 spot moderately bright; no green on the fins or elsewhere. 



April 24. Both fish had the pectoral and pelvic fins with a band of green 8 

 millimetres broad at the tip, fading gradually toward the base of the fin. No green 

 elsewhere. 



May 7. Both fish had the entire pelvics very green, a little paler toward the base. 

 Pectorals green except the basal one-third. Anals green, lighter toward base. 

 Ventral surface with faint green sheen. Border of tail-spot light yellow-green. 

 Individual kept in the dark was a trifle brighter. 



May 23. Both with anals and pelvics fully green, pectorals green except at base. 

 Caudal slightly green. Both slightly green on ventral surface. 



The light not having produced any noteworthy difference in the two fish, the 

 water was now shut off from the dark aquarium and an air- jet used to aerate the 

 water. The temperature of the water was thus raised in this aquarium about 5° C. 

 above that in the light aquarium. 



