THE 



AMERICAN NATURALIST. 



Vol. XXXVllI. J/W/. igo4. 



BREEDING HABITS OF CRAYFISH. 



E. A. ANDREWS. 



Of the breeding habits of the European crayfish much is 

 known, but this is not the case with the American species. The 

 easy assumption that the habits here were essentially identical 

 with those there, has been, possibly, one reason why so little has 

 been put on record regarding our American forms. That there 

 are, however, some considerable differences will ajipear from the 

 following notes made upon that common species Camhanis affims 

 in 1894 and 1900-1903. Though these observations were made 

 upon individuals kept in confinement in the Biological Labora- 

 tory, they may, for the most part, be taken as a guide to what 

 is to be expected from field observations, which still remain much 

 to be desired. 



Sex ratio. — The specimens used were taken from the Poto- 

 mac River in Maryland and when attention was given to the 

 ratio of the sexes it was found that one lot in March 15, 1901, 

 contained 26 females and 14 males while another lot. April 20, 

 1903, contained 39 females and 14 males. While this shows a 

 marked predominance of females over males at those i)eriods and 

 at that locality it is not general, for a lot of eighty of the same 

 species taken in October, 1903, from a pond in Baltimore, con- 



