1978] 
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suggest that the tergal glands might be involved in the chemical trail 
communication of army ants. We have begun to test this hypothesis 
with Eciton hamatum. The pygidial gland secretion of E. hamatum 
has a strong, characteristic smell. The secretion is probably skatole 
(Traniello pers. communication), the substance that gives army ants 
their typical “fecal odor”. Recently Brown et al (1978) demonstrated 
that skatole is an effective growth inhibitor for bacteria and fungi 
and repels insectivorous snakes (Watkins et al 1969). Our first, 
preliminary tests demonstrated that Eciton workers follow artificial 
trails drawn with crushed pygidial glands. When we simultaneously 
offered trails drawn with hindgut contents and pygidial gland 
secretions, the latter were significantly preferred during the first 
minute. When we used trails drawn with secretions of the poison 
gland or Dufour’s gland as controls, the ants always followed the 
pygidial gland trails. We have to stress, however, that these 
experiments must be considered pilot tests. The preliminary results, 
however, are striking enough to warrant a more detailed investiga- 
tion in the future. It is interesting to note that the anatomy of the 
pygidial gland in the African army ant, Dorylus molesta, is quite 
different from that of Eciton and Neivamyrmex (Fig. 25). In this 
species the 7 th tergum is considerably larger than in species of the 
latter genera, and the reservoirs of the pygidial glands do not open 
at the abdominal tip. In Dorylus, however, we found single 
glandular cells with channels opening directly at the anus, a feature 
we have not detected in other ant species (Fig. 25, 26). 
Finally, our morphological study of the pygidial gland of Ve- 
romessor pergandei has led to results that are suggestive of the 
function of this organ. In this species the 7 th tergum is relatively 
small, and as a result the large reservoirs of the pygidial glands open 
at the tip of the gaster (Fig. 27). Veromessor forages in well- 
organized columns (Went et al 1972; Wheeler and Rissing 1975; 
Bernstein 1975). Several observations suggest that these foraging 
columns are organized by a trail pheromone, though no trail 
pheromone gland has yet been identified. Clearly, the large pygidial 
gland has to be considered as a possible source for the trail 
pheromone. 
The function of most of the newly discovered sternal glands is 
unknown. Only in Paltothyrcus tarsatus could we demonstrate 
experimentally that foragers lay a recruitment trail with sternal 
gland secretions (Holldobler in prep.). 
