NO. 9 OLFACTORY SI^-NSK OF INSECTS .MclNDOO 35 



as smelling organs, because they are more highly developed and more 

 advantageously distributed on the antennae in the males so that they 

 inay be of the greatest use in scenting the females. The end pegs 

 also aid in olfaction, particularly when the insect is resting. He does 

 not think that the pore plates in Hymenoptera have an olfactory use, 

 and he regards this view as based on insufficient data. Olfaction in 

 the \'espidae (wasps) is accomplished by the pegs, because the pit 

 pegs are almost absent, while in the bees the pegs and pit pegs both 

 are olfactory in use ; but since the male bees do not have these pegs, 

 the sense of smell is entirely performed by the pit pegs. 



Rohler (1905) made a special study of the antennal organs in a 

 grasshopper, (Try.valis) Acridclla iiasiita L. On the antenniie he 

 found only three kinds of organs, viz : bristles, pegs and pit pegs. Of 

 these three he regards only the pit pegs as olfactory in function, and 

 the females have only about two-thirds as many of them as have the 

 males. This additional number of pit pegs greatly aids the males in 

 finding the females. 



Cottreau (1905) discusses the sense of smell of insects in a pop- 

 ular way, without performing any experiments or citing any refer- 

 ences. He says that the olfactory organs are the pits and papillae, 

 distributed abundantly on the antennae and without doubt in certain 

 regions on the mouth parts. 



In discussing olfaction and antennal sense organs of insects Berlese 

 (1906) seems to infer that there can be no doubt that the antennae 

 are really the seat of the smelling organs. 



In a comprehensive study of the morphology of the chitinous sense 

 organs of Dytiscus rnarginalis, a water beetle, Hochreuther (1912) 

 finds seven dififerent kinds of organs. Of these seven only the hollow 

 pit pegs (hohle Grubenkegel) are probably olfactory in function. 

 They not only occur on the antennae and mouth parts, but a few are 

 found on the thorax and perhaps a few on the coxae of the first two 

 pairs of legs. 



CAUDAL STYLES ("ABDOMINAL ANTENN.^") AS SEAT OF 

 OLFACTORY ORGANS 



Packard (1870) discovered that the caudal styles of the female 

 Chrysopila (a fly) possess a peculiar sense organ. On the posterior 

 edge of the upper side of each style there is a single, large, round sac 

 with quite regular edges. Its diameter is equal to one-third of the 

 length of the style. Dense, fine hairs project inward from its edge, 

 and the bottom of this shallow pit is a clear, transparent membrane 

 devoid of hairs. Since this same insect possesses no antennal organs 



