This gland can either be a discrete structure located bilaterally above each kidney, or a cluster of cells in the head kidney that perform the functions of the adrenal gland. In either case, this organ consists of two cells types, aminergic chromaffin cells and steroidogenic cortical cells[GO].
Comment:
[homology-note] "All craniates have groups of cells homologous to the mammalian adrenocortical and chromaffin tissues, but they are scattered in and near the kidneys in fishes. (...) The cortical and chromaffin tissues come together to form adrenal glands in tetrapods.[well established][VHOG]" xsd:string {date_retrieved="2012-09-17", external_class="VHOG:0001141", ontology="VHOG", source="ISBN:978-0030223693 Liem KF, Bemis WE, Walker WF, Grande L, Functional Anatomy of the Vertebrates: An Evolutionary Perspective (2001) p.518 and Figure 15-9", source="http://bgee.unil.ch/"}