136 THE SENSE ORGANS AND REFLEX BEHAVIOUR 



the tarsi are in contact with distilled water 95 to 100 per cent, 

 response ensued, while without tarsal contact only 1-4 to 13 per 

 cent, response was observed. With paraffin oil the response was 

 very small, while with IM saccharose solution the response varied 

 from 80 to 100 per cent., depending upon the nutritional state of 

 the insects. By means of their tarsi they were able to discriminate 

 between water and saccharose solution and between water 

 and paraffin oil. The oral lobes of the proboscis appear also 

 to be equipped with taste sensillae which are more sensitive to 

 saccharose than are the tarsi. In a subsequent paper (1926a) 

 Minnich states that gustatory hairs are present on the proboscis 

 of Calliphora. A fly, after being abundantly supplied with water, 

 but otherwise starved, does not exhibit any response when 

 distilled water is brought into contact with these hairs. When 

 they are touched with a minute brush moistened with sugar 

 solution the proboscis becomes quickly extended. The sensitivity 

 of these hairs is stated to be so great that a single one, when 

 stimulated in this way, produces the proboscis response. It is, 

 therefore, concluded that a true gustatory response is involved. 

 Minnich subsequently extended these observations while working 

 in the laboratory of Professor K. von Frisch in Munich. Thus, 

 he determined the range of chemical sensitivity of the legs of the 

 blow-fly {Calliphora vomitoria) to Narious sugar solutions (Minnich. 

 1929). In 1931 he published the results of studies on the reactions 

 of the mouth-parts of that same insect. He found that the 

 aboral surfaces of the oral lobes of the proboscis are clothed with 

 marginal hairs which appear to be gustatory in function. The 

 minimum concentration of saccharose which, when applied by a 

 fine brush to the hairs in question, will produce proboscis extension, 

 is about 1/100 M and much higher than that for the legs. The 

 threshold for glucose is at least four to eight times higher than 

 that for saccharose, while lactose was the least effective of the 

 sugars that were tested. The fact that saccharose is sixteen to 

 sixty-four times more effective than lactose suggests that the 

 hair-receptors concerned are chemical sense organs rather than 

 tactile or osmotic in function, since equimolar solutions of these 

 two sugars are similar as regards their viscosity and osmotic 



