No. 516] COPULATION AMONG CRAWFISHES 747 



even resist the attacks of the male, but generally this is not done with 

 much vigor, and very soon after being seized by the male the female 

 passes into a state of passivity, resembling death. 



Hay 2 in a recent paper makes statements which give a 

 somewhat different aspect to the matter. In speaking of 

 an hermaphrodite crawfish he says (p. 228) : 



It might be added that during the time the specimen was kept alive 

 it was seen in conjugation with a female of the same species and a 

 little later was itself seized and held for a short time in the usual 

 manner by a male. The latter, however, is a matter of little importance, 

 as I have several times observed the same thing in the case of two 

 males neither of which was hermaphrodite. 



An adult male of the genus Cambarus is easily dis- 

 tinguished from a female of the same species by his larger 

 chelrc and narrower abdomen, and the sex of any indi- 

 vidual can of course be accurately determined by examin- 

 ing the first two pairs of abdominal appendages. Whether 

 such differences are as readily discriminated by the sen- 

 sory receptors of a crawfish as they are by the human 

 eye is perhaps open to question. According to the quota- 

 tion from Andrews it would appear that a male is able to 

 recognize a female as such, but the statements of Hay 

 might be interpreted in such a way as to lead to the 

 opposite conclusion. 



A series of five experiments was carried out to test the 

 ability of male crawfish to discriminate members of the 

 opposite sex. In the different experiments from two to 

 seven males were separated from females which they had 

 been holding and put together in a flat circular dish 

 (which measured thirty centimeters in diameter and con- 

 tained clean water to a depth of about five centimeters). 

 After such treatment the crawfishes were active for a 

 time and moved restlessly about the dish. During this 

 period of activity one male often tried persistently to 

 copulate with another male, but such attempts were 

 always resisted, and, although individuals were turned 



a Hay, W. P., " Instances of Hermaphroditism in Crayfishes," Smith- 

 onian Misc. Coll., Vol. 48, 1905, Pt. 2, No. 1593, pp. 222-228. 



