OLFACTORY SENSILL^ 131 



precautions. Unless applied in very dilute concentrations, or 

 used at a sufficient distance to ensure adequate dilution by the 

 intervening air, erroneous results may ensue. It is probable that 

 substances of this type may produce merely irritant sensations 

 capable of affecting almost any type of receptor organ, after the 

 analogy of pungent vapours which directly affect the nose, eyes 

 and throat in human beings. It will be obvious that a very 

 erroneous conception may arise with regard to the location of the 

 true olfactory organs of insects, unless adequate precautions are 

 taken to exclude the possibility of a different kind of reaction 

 being involved at the same time. 



In his most recent experiments, using certain kinds of " blow- 

 flies," Mclndoo (1933, 1934) reasserts his previous conclusions 

 regarding the location of the olfactory sense being elsewhere 

 than on the antennae. Among recent workers, Glaser (1927) 

 and Valentine (1931) arrived at very different opinions with 

 respect to other insects. Glaser concluded that olfactory 

 chemoreceptors in Periplaneta are present not only on the antennae, 

 but also on the labial and maxillary palpi. The antennae, he 

 claims, are capable of longer distance olfactory perception than 

 either of the two pairs of palpi. Valentine carried out a number 

 of experiments with reference to sex responses in Tenehrio molitor 

 (the meal-worm beetle). He found that individuals of both sexes 

 responded to a glass rod smeared with gland secretion pertaining 

 to the opposite sex, provided the antennas were intact. Males 

 without antennae were unable to discover the females and they 

 betrayed no responses when brought into close proximity to 

 individuals of the opposite sex. Similar results, it may be added, 

 were obtained when using food stimuli (aqueous bran extract). 

 He was further able to show that olfactory perception was located 

 in the apical four segments of the antennae. When employing 

 essential oils of clove, bergamot and thyme, he found that they 

 exercised an irritating effect, and he concluded that they reacted 

 upon other senses besides that of olfaction and also affected the 

 respiratory system. A summary of the subject of olfactory 

 receptors in insects is given by Marshall (1935), to which the 

 reader is referred for a fuller reference to the literature. At the 



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