The results obtained by many authors on the GeSeIn vitreous system, in particular, those concerning the variations of the glass transition temperature, T_g, with the average coordination number, Z, are investigated from a new perspective. From the assumption that In atoms participate in the formation of In₂Se₃microclusters, we show that the variations of T_g with Z of the alloy are consistent with Sreeram's relationship and with Tanaka's structural transition model. We conclude that In is threefold coordinated with Se atoms to form In₂Se₃ microclusters and that these microclusters do not contribute to the variations of T_g with the alloy composition.