COMMUNICATION AMONG INSECTS McINDOO 



559 



for allurement (fig. 4, D, s), and in the case of other species for 

 defense (fig. 4, E, s). 



The dorsal scent gland of the honeybee (fig. 2, p. 551) belongs to a 

 fourth type and is one of the most highly developed of the gcent 

 glands used for purposes of recognition. 



5. ANTS RIVAL DOGS IN TRACING TRACKS 



For ages the dog's nose has been considered the most acute smell- 

 ing organ among all animals, but a review of the literature shows 

 that the " noses " of insects are close competitors and possibly second 

 to none. It is well known that dogs can trace the tracks of man and 

 animals merely by smell, as was recently demonstrated by Buytendijk, 

 a Dutch physiologist. During the World War a lively interest was 

 taken in the breeding and 

 training of police dogs. 



Those used were such reli- /" ^"*''^*'*''**<v,-uj:;v'' X 



able trackers that they were 

 known to find the scent un- 

 der snow Avhen bloodhounds 

 were useless, and they ren- 

 dered great aid in bringing 

 in the wounded. 



On a level, sandy place in 

 Amsterdam a boy followed 

 the route indicated by the 

 solid line in Figure 5, begin- 

 ning at a tree B, and ending 

 at a laboratory L. A strong 

 wind was blowing in the 

 direction indicated by the 

 arrow W. At T were two 

 street cars, and at H two 

 huts used by construction workers. As soon as the boy had finished 

 the trip a police dog was led to the tree, allowed to smell the boy's 

 cap, and started on the trail made by the boy. The dog followed 

 the route indicated by the dotted line. Between the tree and the 

 street cars the dog followed to the right of the boy's trail, apparently 

 because the wind had scattered sand on which the boy had walked. 

 In the lee of the street cars he followed the trail closely. Where the 

 boy had turned at X the dog had some difficulty, as shown by his 

 windings. Just before reaching the huts the dog lost the trail, 

 evidently because many people were walking about, but soon found 

 it and followed it to the laboratory. 



For information regarding the ability of dogs to discriminate 

 between the body odors of people, Buytendijk carefully tested Albert, 



Figure 5. — Diagram illuytrating experiment to test 

 the ability of a police dog to follow the trail of 

 a human being. (After Buytendijk) 



