66 NATURAL HISTORY OF AMIA CALVA LINN.EUS. 



going apparently into the soft ooze beneath this vegetation. There was no per- 

 ceptible disturbance of the bottom ooze and no cloudiness of the water. The fish, 

 especially those dropped in head first, disappeared into the earth with incredible 

 swiftness, as if by magic, and left no trace behind them." 



3. Nest-building. A. SEASON. During the four seasons covered by my notes 

 the nest-building, as measured by the first and last nests found, was as follows : 



1898, April 19 to May 1. 



1899, April 24 to April 30. 



1900, April 23 to May 16. 



1901, April 24 (about) to June 1. 



In 1900 and 1901 the nest-building was interrupted by cold weather late in 

 April and in May, and was resumed upon the return of warmer weather. The brood- 

 ing of the young continued until June 20 in 1901 and possibly beyond this. The 

 earliest date at which I have taken eggs is April 15, and they were not over two days 

 old. As a rule the middle of April and the middle of June mark the limits of the 

 breeding season in this locality. Further records as to the breeding season are to 

 be found in Hallock (77), FuUeborn ('94), Dean ('96, '98), and ^Vhitman and 

 Eycleshymer ('97). 



It would be most convenient if one were able to fix the beginning of the 

 nesting season by referring it to definite stages in the growth of aquatic or shore 

 plants or to the appearance of other and more readily observed aquatic animals, 

 such as turtles or breeding frogs or toads. I have made numerous attempts to do 

 this, but without uniform results. A relation established in one season may not, 

 and usually does not, hold for the succeeding season. 



ShaUow water on the spawning grounds is subject to great daily variations in 

 temperature. The greatest variation noted is 7.5 C. (9.5 C. at 8 A.M. and 17 C. at 

 3 P.M.). The water has usually reached its maximum temperature at about 6 P.M., 

 and I have made use of temperatures taken at that hour and at a depth of 20 centi- 

 metres, and have found the greatest activity in nest-building to occur at tempera- 

 tures of 16 C. to 19 C., measured in this way. The following table shows the rela- 

 tion of nest-building to temperature. It is made by adding the empty nests found 

 during the seasons of 1898, 1899, and 1900 on all those days when the water was of 

 the same temperature. Temperatures are expressed to the nearest degree. In the 

 upper row the temperatures used are those of the day on which the nests were 

 found; in the lower row the temperatures are those of the day before, and prob- 

 ably express more nearly the temperature of the night on which the nests were 



