102 ENTOMOLOGY 
far as we can judge from our own experience. Though it is 
easy to demonstrate that the antennz, for example, are olfac- 
tory, it frequently happens that the antennz bear several dis- 
tinct forms of sensory end-crgans, so minute and intermingled 
that their physiological differences can scarcely be ascertained 
by experiment but must be inferred from their peculiarities of 
structure. Schenk, however, has arrived at precise results 
by comparing the antennal sensilla in the two sexes, selecting 
species in which the antennz exhibit a pronounced sexual 
dimorphism, in correlation with sexual differences of behavior. 
Taking Notolophus (Orgyia) antiqua, in which the male seeks 
out the female by means of antennal organs of smell, he finds 
that the male has on each antenna about 600 sensilla ccelo- 
conica and the female only 75; similarly in the geometrid Fido- 
nia, in which the ratio is 350 to 100. The sensilla styloconica, 
also, of these two genera are regarded as olfactory organs. 
These two kinds of end-organs are not only structurally adapted 
for the reception of olfactory stimuli, but their numerical dif- 
ferences accord with the observed differences in the olfactory 
powers of the two sexes, there being no other antennal end- 
organs to enter into the consideration. 
Assembling.—It is a fact, well known to entomologists, 
that the females of many moths and some beetles are able by 
exhaling an odor to attract the opposite sex, often in consid- 
erable numbers. Under favorable conditions, a_ freshly 
emerged female of the promethea moth, exposed out of doors 
in the latter part of the afternoon, will attract scores of the 
males. A breeze is essential and the males come up against 
the wind; if they pass the female, they turn back and try again 
until she is located, vibrating the antennze rapidly as they near 
her. The female, meanwhile, exhales an appreciable odor, 
chiefly from the region of the ovipositor, and males will con- 
gregate on the ground at a spot where a female has been. If 
one of these males is deprived of the use of his antennz, how- 
ever, he flutters about in an aimless way and is no longer able 
to find the female. 
