202 
Psyche 
[Vol. 91 
Results 
The metapleural gland is a paired structure. Each side consists of 
a cluster of glandular cells, and each cell is drained via a duct into a 
membranous collecting sac that Tulloch et al. (1962) called secretory 
recess. The collecting sac leads directly into the storage chamber or 
atrium (receptacle, sensu Tulloch et al. 1962), a sclerotized cavity. 
Externally the metapleural gland is often marked by a pronounced 
vault (bulla), and a slit-shaped opening to the outside (Fig. 1). 
Although the metapleural gland is present in most ant species, it 
nevertheless varies greatly among them in size and shape (Figs. 2 & 
3). Table 1 lists all of the ant species for which we obtained complete 
series of longitudinal sections through the mesosoma. The speci- 
mens were fixed in alcoholic Bouin or Carnoy, embedded in 
methylmethacrylate and sectioned 6 to 8 p thick. The staining was 
Azan (Heidenhain). We attempted to obtain approximations of the 
number of glandular cells either by counting the cells with clearly 
visible nuclei or by counting the number of duct openings in 
successive sections. 
The data reveal a considerable variation in the size of the 
metapleural gland among different species. Even more significantly, 
our study established that the gland is absent in Oecophvl/a 
/onginoda and O. smaragdina (Fig. 4), in all species of Camponotus 
and Po/vrhachis sectioned, and in Dendromyrmex chartifex (Tab. 
1 ). 
We extended this list by an additional survey of the external 
features that indicate the presence of the metapleural gland, using 
light-stero-, and scanning electrone microscopy. Of 27 species of 
Camponotus investigated, only C. gigas showed a slit-shaped 
opening in the posterior metapleural region (Fig. 5c). In all other 
Camponotus species the metapleural gland is clearly absent (Fig. 5a, 
b; Tab. 2). This confirms the suggestion of Ayre and Blum (1971) 
based on external inspection of Camponotus pennsvlvanicus 
workers that this species might not possess a metapleural gland. In 
none of the species of Polyrhachis investigated did we detect any 
signs of a metapleural gland (Tab. 2). In addition our study revealed 
that in several species whose workers and queens have well- 
developed metapleural glands, the males do not possess this organ; 
whereas in other species the males have large metapleural glands 
(Tab. 1). 
