750 



THE AMERICAN NATURALIST [Vol. XLIII 



Ohidester 4 has recently shown that the general activity 

 of crawfishes is greater at night and it would therefore 

 seem probable that copulation would be more likely to 

 take place in the dark than in the light. In order to ascer- 

 tain if this supposition was correct, two oblong dishes 

 were placed side by side in front of a window and were 

 filled to a depth of five centimeters with water which was 

 of the same temperature in the two dishes (11° to 14° C. 

 in different experiments). One of the dishes was allowed 

 to remain exposed to strong light, but not to the direct 

 rays of the sun, and the other was completely enclosed in 

 a tight wooden box which was painted black on the inside 

 and covered by a movable lid. In each experiment two 

 pairs of crawfishes which had been copulating or attempt- 

 ing to do so were isolated and a separate male and female 

 placed together in each dish, after which their behavior 

 was noted at short intervals of time. In order to elimi- 

 nate the effects due to the individuality of any particular 

 crawfish, the individuals of each quartette were changed 

 about as much as possible in successive trials. After the 

 first copulation, the male was changed from the dark dish 

 to the one in the light, and the male which had been in the 

 light took his place; after the next trial the pairs were 

 interchanged, and finally the two females were changed 

 about. By this method of procedure there was an oppor- 

 tunity to compare the rapidity of copulation in the light 

 and in the dark. The results of the experiments are 

 given in Table I. 



Table I. 



rdmnged L I L ! D i D D fe P 

 changed L E L D L D P 



rotes on the Daily Life and Food of Cambarus 

 Nat., Vol. 42, 1908, No. 503, pp. 710-716. 



