632 THE SENSES AND SENSORY ORGANS. 



The next day Will made the same experiment with sugar, 

 followed by gypsum (dolomite). The Wasps licked the dolo- 

 mite until the evening, before the idea dawned upon them that 

 the insoluble material was not adapted for food. 



Will purposely selected these three substances on account 

 of the similarity of their appearance, and the absence of any 

 odour to guide the insects. 



The avidity for sweets exhibited by Flies is well known, and 

 it is quite evident that they are guided in the selection of 

 food by the sense of taste. I have not, however, made any 

 special experiments on the subject. 



If the determination of the seat of the sense of smell is dim- 

 cult, it is still more difficult to locate the sense of taste in any 

 special organs. I have already given reasons for supposing 



Fie. 83. A, one of the large gustatory setns from the oral lobe of the proboscis 

 of the Blow-fly; />, a transverse section of a similar seta; g, ganglion cell; 

 A, hypodermal cells. 



that the oral lobes and maxillary palpi are both concerned as 

 organs of taste (p. 403). 



Will considers that the end organs of taste must necessarily 

 come into contact with the dissolved food, and that the setae 

 which subserve this function must be either perforated at their 

 top or grooved at the side. As I have already remarked, the 

 setae of the palpi are perforated, and those of the oral lobes are 

 grooved on one side. A comparison of the end organs of 

 the palpi of the Fly with those of the antennae (PI. XLL, 

 Figs. 2 and 4) shows a marked difference, and, as might perhaps 

 be expected from their position, the palpi of the Muscidae are 

 much less developed than those of most Insects. 



The end organs connected with the grooved setae on the oral 



