130 THE SENSE ORGANS AND REFLEX BEHAVIOUR 



the receptors must be located on some other part of the body, 

 since after all antennal function was eliminated the insects were 

 still responsive to an extent of 42 per cent. 



The series of experiments conducted by von Frisch (1921) with 

 regard to the olfactory responses of the hive bee showed that 

 this insect is just as insensible to odours when the eight terminal 

 segments of the antennae are excised as when the entire appendages 

 are amputated. He emphasises the fact that bees trained to 

 respond to a specific odour no longer respond to that odour after 

 amputation of their antennae. The absence of the olfactory 

 reaction, he maintains, is due to loss of the organs of smell, and not 

 to shock caused by the operation. In support of this conclusion he 

 points out that bees conditioned to respond to a certain colour still 

 seek that colour, and no other, after deprivation of their antennae. 

 It is further noteworthy that the most conspicuous antennal 

 sensillae are of the placoid type, and these are located on the last 

 eight flagellar segments, ^'on Frisch concluded on these grounds 

 that the olfactory sense resides in the antennae and that the 

 placoid sensillae are the chief receptors involved. Mclndoo 

 (1914), on the other hand, came to the conclusion that the antennae 

 are organs bearing little or no relation to olfactory sensation and 

 that the true organs concerned are the so-called olfactory pores 

 which are distributed over various regions of the body. 



As Snodgrass has pointed out, Mclndoo's experiments were 

 conducted under confined conditions, whereas those of von Frisch 

 related to bees free in the apiary. Furthermore, the latter 

 observer experimented with floral extracts, whereas Mclndoo 

 used more powerfully smelling volatile oils. There is, therefore, 

 a very evident difference in the experiments in the two cases. 

 Mclndoo's observations only showed that antennaless bees can 

 perceive strong odours when in close proximity to them, while von 

 Frisch demonstrated that bees so treated are unable to sense the 

 presumably much milder floral odours when in a state of natural 

 freedom around the apiary. It appears likely therefore that, in 

 all experiments dealing with olfactory responses, the use of 

 powerful or irritant compounds, especially those which do not 

 enter into the normal experience of a given insect, needs special 



