Bulletin Wisconsin Natural History Society [Vol. 13, No. 1 
38 
That copulation is due to a chance contact and not to any 
sense that would lead to a seeking on the part of the male is shown 
by the following experiment. A number of individuals of both 
sexes were placed in a cage, allowed to remain undisturbed, and 
the total number of copulations recorded during a period of two 
hours. During the next two hours, as soon as a pair separated, 
they were forced to move about by being poked with a wire so 
that contact with the others became necessary. The total number 
of copulations for the second period exceeded that of the first by 
more than a third. It is true also that more copulations take 
place in a small cage than in a larger one. 
There is reason to believe that sex discrimination is accom- 
plished by the sense of touch and smell and that it is localized 
in the antennae and palps. As has been pointed out, a male 
will grasp at any moving individual, regardless of the sex, which 
comes in contact with the posterior end of his body. Evidently 
sex discrimination is not located here. If, however, the antennae 
and palps are removed from an unexcited male and he is liber- 
ated in a cage with females no motions are observed which would 
indicate sexual excitement, while there is every evidence of a 
continued sexual excitement when the antennae and palps are 
removed from a previously excited male and he is again liber- 
ated with females after the operation. The excited individual 
will attempt to mate with every one with whom he comes into 
contact, male or female. It seems, therefore, that it is by means 
of the antennae and the palps that a male is able to recognize, 
first, individuals of the same species, second, the distinction be- 
tween males and females. The sense of hearing is obviously ruled 
out in sex discrimination because there are no special organs in 
Ceuthophilus for receiving or producing sounds. The sense of 
sight is also not a factor to be considered, since there is no sexual 
excitement until tactual contact has been established. 
c. Reactions to External Stimuli During Copulation 
To induce copulation it was necessary to keep a pair in weak 
light until they had come into contact and so had become sexually 
excited, but afterward they were indifferent to a reasonable amount 
of stimulation to which they would have readily responded under 
