Ants, and social insects in general, are characterized by their very well developed exocrine system. According to their cellular arrangement, the numerous glands either belong to the epithelial type, or are composed of bicellular units, each comprising a secretory cell and a duct cell. The ultrastructural organization with regard to the uptake, biosynthesis and discharge of the secretory products is very similar in both types, and generally involves surface increasing foldings of the plasmalemma. The cuticle, that forms part of each glandular cell, is mostly provided with pore canals. Pheromone producing glands are characterized by numerous mitochondria, a well developed Golgi apparatus and an extensive smooth endoplasmic reticulum in their secretory cells. The often abundant multilamellar inclusions may correspond with secretory material. Glands producing venomous substances or performing digestive functions, on the other hand, are characterized by their well developed granular endoplasmic reticulum.