“…It characteristically consists of small monopolar neurons ∼15 µm in diameter, which in Neognathae with well‐developed ION form a lamina around a central neuropil containing their dendrites (Clarke & Caranzano, ; Cowan, ; Güntürkün, ; Li & Wang, ). The morphologically different ectopic centrifugal neurons, which lie outside the proper ION, are more heterogeneous in size and generally multipolar (Clarke & Cowan, ; Cowan & Clarke, ; Hayes & Webster, ; Li & Wang, ; Médina, Repérant, Miceli, Bertrand, & Bennis, ; O'Leary & Cowan, ; Weidner, Desroches, Repérant, Kirpitchnikova, & Miceli, ; Weidner, Repérant, Desroches, Miceli, & Vesselkin, ; Wolf‐Oberhollenzer, ). The ION presents a high variety of morphologies with different levels of complexity, but in most species (with some noteworthy exceptions such as Procellariiformes and Pelicaniformes) it is at least clearly distinguishable as a nucleus (Gutiérrez‐Ibáñez et al, ).…”