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 diffi- 
cult, it is still more difficult to locate the sense of taste in any 
special organs. I have already given reasons for supposing 
Fic. 83.—A, one of the large gustatory sete from the oral lobe of the proboscis 
of the Blow-fly; Z,a transverse section of a similar seta; g, ganglion cell; 
h, 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 sete 
which subserve this function must be either perforated at their 
top or grooved at the side. As I have already remarked, the 
sete 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 antenne (Pl. XLI., 
Figs. 2 and 4) shows a marked difference, and, as might perhaps 
be expected from their position, the palpi of the Muscide are 
much less developed than those of most Insects. 
The end organs connected with the grooved setz on the oral 
