10 THE NORTH AMERICAN SPECIES OF DROSOPHILA. 
been removed. But when the female is ready to mate, she will mate 
with a wingless male almost, if not quite, as readily as with a normal 
winged one. 
An extensive series of experiments with various mutant types 
(Sturtevant, 1915) indicated that neither males nor females exercised 
any ‘“‘choice”’ of mates with respect to the characters studied. Usually 
the mutant-type is less active than the wild-type. In such a ease, 
the mutant male mates less often than does the wild-type male, since 
he courts less vigorously and persistently. But the mutant female is 
mated with more often than is the wild-type female, since she is less 
active in running away from the male. 
SEX RECOGNITION BY THE MALE. 
All attempts to induce courtship by means of visual or of olfactory 
stimuli alone have failed in Drosophila. Mating occurs in the dark, 
indicating that sight is not necessary. Males without antenne will 
mate, and Barrows’s experiments (see above) indicate that the organs 
of smell are located in the third antennal joint. Yet there is evidence 
that both sight and smell may play a part in the process. ; 
I compared the time before copulation occurred in two parallel 
series of pairs of D. melanogaster. One series was placed in clean 
vials; the other in vials in which another pair had just copulated. 
The second series mated significantly sooner, on the average. This 
can only mean that olfactory stimuli had hastened sexual excitement. 
When a male of D. melanogaster is courting a female she frequently 
walks or flies away. He orients toward her and follows her accurately 
if she is only a few millimeters away, but never orients accurately if 
she is as much as a few centimeters away. In the latter case he often 
becomes excited, and shows movements characteristic of courtship; 
but he finds the female again only by accident. This behavior is not 
changed if one antenna is removed. Circus movements do not then 
occur when the male becomes sexually excited, and the female, if she 
is close enough, is followed as accurately as before. This seems to me 
to indicate that orientation toward the female is by means of visual 
stimuli. This view is borne out by the fact that sexually excited 
males will sometimes orient toward and follow other males, though 
only rarely does one male cause sexual excitement in another one. 
The hypothesis is also in agreement with Barrows’s observation that 
orientation toward olfactory stimuli (food) occurs at distances much 
greater than those at which a sexually excited male can orient toward a 
female. 
The failure of olfactory stimuli alone to produce courtship, the fact 
that males without antenne will mate, and some observations of normal 
courtship, all suggest that tactile stimuli may be involved; but no 
direct evidence for this conclusion is at hand. 
