No. 516] COPULATION AMONG CRAWFISHES 749 



upon the ' ' chance ' ' coming in contact of two individuals 

 which are in proper physiological state. On five differ- 

 ent occasions when the aquarium, which contained two 

 hundred crawfishes, was visited and no pairs were found 

 to be copulating or attempting to do so, all the individuals 

 were dragged into the center of the aquarium and heaped 

 together in a pile. They were then allowed to remain 

 undisturbed for half an hour. During this time there was 

 an active scramble and many individuals necessarily came 

 in contact with each other. In all the experiments from 

 three to five pairs were found to be in copulation at the 

 end of the half hour. These observations showed that 

 individuals had been present in the aquarium which were 

 in the proper physiological state for copulation, for as 

 soon as they came in contact with each other the usual 

 mating reaction took place. 



There are many factors which might possibly exert an 

 influence on the copulatory reflexes of a crawfish and it 

 is easily conceivable that such stimuli as temperature, 

 light and chemical substances might be of importance in 

 this connection. In regard to temperature Bell 3 has ob- 

 served (p. 625) that, after a number of individuals had 

 been warmed, 



The males showed marked sexual activity, rushing up to the females, 



of their vigorous resistance. One of the males did succeed in turning 

 a female on her hack twice, although she struggled violently to escape — 



He concluded that, " the rise of temperature seemed to 

 stimulate the males to sexual activity but not the fe- 

 males." During the present experiments it was observed 

 that there were fewer cases of copulation when the tem- 

 perature of the water in the general aquarium was below 

 ll 3 C. than when the temperature was above that point. 

 Apparently temperature is of some importance as exert- 

 ing an inhibitory or excitatory action on the copulatory 

 impulse. 



8 Bell, J. C, " Reactions of the Crayfish," Harvard Psychol. Ser., Vol. 

 2, 1906, pp. 615-644. 



