CONJUGATION IN THE CRAYFISH, CAMBARUS AFFINIS 241 
was hooked so as to lie diagonally, that is, on the right his hook 
was in the female's third leg and on the left in the second leg. 
Half an hoar later, however, the male had hooked straight and 
so continued. Thus at least all the early and possibly all the later 
stages of conjugation may be carried on with a dead female, 
which emphasises the passive nature of the female's behavior 
in normal union. 
Again when the males were bound with chelae closed and limbs 
in the posture assumed by a female in conjugation, other males 
with bound chelae were excited by contact and, without the usual 
initiatory use of the chelae, even mounted upon the supine, bound 
males and endeavored to carrj- on conjugation. 
It is thus possible that from the crayfish standpoint the only 
difference between the sexes is a difference in behavior and not a 
difference in form, and moreover a difference received by muscle 
and touch sense and not in effect upon any of the other sense 
organs.- 
The crayfish is thus much like the amphipods studied by Holmes 
who found, ''The different reactions of the two sexes to contact 
with other individuals is the factor which effects the union of the 
males with the females. 
Coming to a more detailed description of the processes of con- 
jugation, we shall describe first the behavior of the female and then 
that of the male and divide his activities into the following 
groups: (1) Seizing; (2) Turning; (3) Mounting; (4) Claw clasp- 
ing; (5) Erection and locking of the stylets; (6) Crossing of fifth 
2 The observations of Chidester upon the craytish, Cambarus bartonius, confirni 
this point of view, for he observed that these males repeatedly grasped males and 
even, despite their struggles, turned them and attempted conjugation. The 
females when seized firmly ceased to struggle and lay passive. lie inferred that 
the males did not recognize the females. 
' After this paper was ready for press appeared the account of the experiments of 
A. S. Pearse, in the American Naturalist, December 1909, in which the conclusion 
is independently reached that the crayfish has "little or no power of sex discrimi- 
nation." His observations were made chiefly upon Cambarus virilis, and make it 
probable that all craj^fish lack means of acting differently toward males and females 
till they are in contact with them and are influenced by their sexually different 
responses, in the fields of touch and pressure. 
