532 William Morton Barroius 



Of fourteen flies which were thus tested all with one exception 

 failed to find the food within fifteen minutes. In the exceptional 

 case food was found in twelve minutes, but the insect's course was 

 such that it obviously came to the food by accident. During these 

 experiments the flies were carefully watched, and although many 

 of them came within i cm. of the food, they did not find it. 



To test this matter further, four of the flies with defective anten- 

 nae were allowed to wander in a small glass tumbler until they 

 found the food, which they apparently did by accident. When 

 one foot of the fly touched the food or a small drop of water the 

 tongue was immediately put down and the animal began feeding. 

 It is not impossible that two transparent hairs which are found 

 beneath the claws of each front foot, and have the appearance 

 of sense hairs, may be instrumental in giving rise to this feeding 

 reaction. It therefore seems certain that the sense of smell is 

 absent, or at least greatly reduced, in flies which have lost the 

 terminal joints of both antennae. In order to determine the rela- 

 tive time taken to find food by flies with and without the terminal 

 segments of the antennae, six normal flies were admitted to the 

 chamber and the time recorded which elapsed before they reached 

 the food. These flies were then operated apon; the distal seg- 

 ments of both antennae were cut oflF and they were allowed to 

 rest twenty-four hours, when they were again tested and the time 

 similarly recorded. The results of these experiments are given in 

 Table VIIL 



From this table it will be seen that the normal hungry fly finds the 

 food in about two and one-half minutes, while the same fly after 

 having been operated upon seemed unable to locate the food. 



We may conclude: first, that Drosophila does not find its food 

 by sight, but by smell, and when this sense is lost it reaches the 

 food only by accident; and, secondly, that the olfactory sense 

 organs — at least those which are concerned with finding food — are 

 localized in the third or distal segment of the antenna. 



The fact that in Drosophila the antennae are the principal 

 organs concerned in the reception of olfactory stimuli and that 

 they are symmetrically placed on the body of the animal, leads to 

 the conclusion that these flies orient to odorous centers in the way 



