IO2 ENTOMOLOGY 



far as we can judge from our own experience. Though it is 

 easy to demonstrate that the antennae, for example, are olfac- 

 tory, it frequently happens that the antennae bear several dis- 

 tinct forms of sensory end-organs, 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 antennae 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 antennae 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 antennae, how- 

 ever, he flutters about in an aimless way and is no longer able 

 to find the female. 



