THE AM ERIC AX XATURALIST. [Vol. XXXVIII. 



tained 41 females and 39 males. Even where the females are 

 more abundant there is no probability of the eggs going without 

 fertilization since it was found that one male unites with several 

 females. 



Time of sexual union. — When specimens were taken in 

 February and put into tanks some unions occurred at once while 

 others were deferred till March. When the sexes were kept 

 separate till March 6 and then put into one tank, unions took place 

 March 6, 7, 8, 9, 10 and 11. After that there were occasional 

 unions, especially of the younger and smaller animals, up to 

 April 2. Besides these observed unions in February, March 

 and April it would seem that there is an Autumnal pairing, in 

 place of or in addition to the Spring pairing. Several small 

 specimens reared from eggs laid in the Spring were found to 

 pair early in October of the same year ; while at that same time 

 pairs of larger size were taken in a pond in Baltimore. More- 

 over specimens from Washington, D. C, in 1894, in November, 

 were seen to pair as soon as they were put into a shallow dish. 



Description of sexual union. — The union of the sexes in 

 C. affinis was first observed in 1 894, and briefly described in the 

 Amencan Naturalist in 1895. The same phenomena have been 

 repeatedly witnessed in successive years and there is no doubt 

 that in this species of crayfish the sperm is transferred from the 

 male to an external seminal receptacle upon the female where 

 it is stored up till the time that the eggs are laid. There is no 

 copulation or use of intromittent organs such as takes place in 

 the crabs ; nor on the other hand is there any such vague 

 attachment of spermatophores as has -been described in the 

 Kuropean crayfish, Astacus. 



In captivity the union lasts from two to ten hours and either 

 the male or the female may repeat the process with other 

 individuals. 



When a female is put into a dish in which a male has been 

 kept till he is accustomed to it he soon seems aware of the 

 presence of the female and does not act as he does when only 

 males are introduced. The preliminary steps toward union are 

 soon taken. The male advances with ready claws and seizes 

 the female, sometimes gently. The female retreats or, when 



