CAMPANIFORM SENSILLM 



129 



The delicacy of the coveriii^^ iiieiiibrane of the campaniform 



sensilla suggests that, in many cases, these organs may function 



as olfactory receptors. They occur distributed over the body 



and on the wings, halteres, legs, antenna?, palpi, sting, cerci and 



other parts in different orders of insects. This very wide range 



of location has rather argued in the past against any idea that 



they are of olfactory significance. They have been assumed 



by some authorities to be receptors of vibrations or of changes 



in atmospheric pressure, but the only experimental evidence 



relative to their function is afforded by Mclndoo. While it 



appears from the results of his extensive 



observations that these sensilla? function as 



olfactory receptors, his data are insufficient 



to invalidate the conclusions of other skilled 



experimenters that olfactory sensilhie, of 



different types, are also present and are 



chiefly located on the antenniE. Certain 



experiments by Minnich (1924) may be 



quoted here, since they appear to afford an 



example of how the two points of view 



may be reconciled. He showed that by 



coating one antenna of Pieris rapcu either I^'ig. 57. Diagram of 



.,, ,. .., . . p «. an olfactory (cam- 



with vasehne or with a mixture ot pararhn paniform) ' sensilla, 



and vaseline, or by directly amputating the according to Mclndoo. 



1 lo J. ' .• . 1 • • c, Cuticle ;/>, olfactory 



appendage, oliactory reaction to apple juice p^^.^ . ^^ sense-cell. ' 



was only affected by 6 per cent. When 



both antenna? were treated in a similar manner the response was 



reduced by 58 per cent. Minnich states that the treatment 



described resulted in no general abnormal behaviour ; even with 



amputation of the antennae little disturbance was noted, and 



clear-cut results were obtained. Although the histology of the 



sensilla? involved was not investigated, Minnich concludes that 



the abundance of these structures on the antenna?, taken in 



conjunction with the reactions mentioned, indicates that these 



appendages represent probably the most important olfactory 



region of the body. On the other hand, he points out that the 



responses of the insect show that a considerable proportion of 



K.A. ENTOMOLOGY. 5 



