138 THE SENSE ORGANS AND REFLEX BEHAVIOUR 



wherein the flies are easily able to distinguish between chemically 

 pure saccharose water and distilled water when the tarsi are 

 about 3 mm. distant from these liquids. The act of touching 

 the tarsi by means of a brush, moistened with the substance to 

 be tested, produces the initial stimulus and brings the liquid 

 almost in contact with certain campaniform sensillae in the tarsi. 

 He further states that a high response resulted by merely 

 touching the tarsi with a needle, the proboscis being protruded 

 when the sugar solution was 3 mm. away. It is possible, 

 therefore, that the tarsi of the blow-fly, like the antennae of the 

 bee, bear both contact and distance receptors. For other insects, 

 tarsal sensoria are described by Eltringham (1933) as being 

 extremely slender, thin-walled tubes in the butterfly Pyrameis 

 atalanta (Fig. 59). 



The work of Minnich opened up a new field of experimentation 

 in so far as insects are concerned. It is noteworthy that several 

 previous investigators have shown that the walking legs in the 

 higher Crustacea are sensitive to contact with foods and other 

 chemical stimuli. B. M. Patten has also demonstrated that the 

 modified anterior legs of the whip-tail scorpion are likewise 

 sensitive to water and other chemical stimulation. In the 

 light of the foregoing evidence, Minnich considers that contact 

 chemoreceptors, located in the distal extremities of the thoracic 

 legs, are of general occurrence among Arthropods. 



