Electron microscope studies on soma-somatic interneuronal junctions in the corpus pedunculatum of the wood ant (Formica lugubris Zett.).

1. The corpora pedunculata of the wood ant (Formica lugubris Zett.) contain densely packed neuron perikarya which are separated by ultrathin glial sheaths. 2. These glial sheaths are occasionally interrupted by round holes with an average surface area of 2.64 µ2. The holes are designated glial windows since they represent intracellular gaps of glial cytoplasm. 3. The glial windows allow soma-somatic interneuronal junctions. Of all adjacent neurons in a selected neuron pool, only 42% were interconnected by such junctions. 4. The intercellular space at the soma-somatic junctions has an average diameter of 30 A; occasionally, it is collapsed and an external compound membrane ensues. The junctional membranes are characterized by the presence of a subunit pattern of cross-directional electron-opaque lines with a 50- to 70-A periodicity. 5. Morphological signs of chemical transmission are absent in these junctions. On the other hand, there is a striking similarity in structural organization between soma-somatic junctions and electrical synapses described in other species. Therefore, it is suggested that these cell contacts of the ant's "cerebral cortex" are another form of electrical junction. 6. The close proximity of the junctions to the cell nucleus is noted. Its significance could not be ascertained. 7. The suggestion is made that glial windows may have dynamic properties and may intervene in the regulation of interneuronal transfer of information.