292 
Psyche 
[December 
discovered that the cues responsible for “binding” the follower 
behind the leader ant include both a surface pheromone and 
mechanical stimuli. Although we could extract this surface phero- 
mone, we were not able to identify its anatomical source; all 
experiments with secretions from the known exocrine glands had 
negative results. After the recent discovery of the pygidial gland in 
Pachycondyla we have begun to conduct tandem running experi- 
ments with Pachycondyla crassa* and P. harpax*, using dummies 
contaminated with pygidial gland secretions. Our preliminary re- 
sults strongly indicate that pygidial gland substance might be the 
source of the tandem running pheromone in these species. 
In the doryline army ants raiding and emigrations are conducted 
along chemical trails deposited by workers. For Neivamyrmex, 
Watkins (1964) and Watkins et al (1967), and for Eciton hamatum, 
Blum and Portocarrero (1964), identified the hindgut as the source 
of the trail pheromone. In addition, Chadab and Rettenmeyer 
(1975) and Topoff and Mirenda (1975) demonstrated that besides 
the relatively long-lasting hindgut trail-substance, other signals 
(possibly more volatile secretions) are involved in the organization 
of “mass recruitment” in Eciton and Neivamyrmex. 
We believe that our morphological investigations provide new 
possibilities for the analysis of chemical communication in army 
ants. Both Neivamyrmex and Eciton have large pygidial glands with 
distinct reservoirs (Fig. 22, 23). The postpygidial gland is smaller, 
but still considerably larger than in most of the other investigated 
speciesf . In both army ant species the 7 th tergum is relatively small. 
Therefore, the reservoirs of the pygidial gland and postpygidial 
gland open directly above the anus at the abdominal tip (Fig. 23). In 
workers (all castes) of Eciton the dorsal membrane near the exits of 
the reservoir of the pygidial glands is conspicuously modified to a 
brush-like structure (Fig. 24). These morphological features strongly 
* P. crassa was observed tandem running by W. L. Brown, Jr. (pers. communica- 
tion) at the western base of Ubombo Mts., Zululand, and by B. Holldobler in 
Shimba Hills Reserve (Kenya). P. harpax was observed tandem running by S. 
Levings (pers. communication) on Barro Colorado Island, Panama. 
t Whelden (1963) described two glands at the extreme posterior end of the gaster of 
Eciton burche/li workers. Although the description is not very accurate, from his 
drawings we can conclude that he found the pygidial gland and postpygidial 
glands. 
