Fig. 1

A transverse diagrammatical representation of the development of the myogenic electric organ (mEO) in Brachyhypopomus gauderio [1]. A pair of dense cell masses constituting an electric organ primordium (ep) develop on the ventral side of the somite muscle (sm) at around 3.5 to 4 days post-fertilisation. During the following days, these cell masses move downwards into the ventral fin fold (vff), and approximately each day a pair of electrocytes (e) are formed behind them, in the space between them and the somite muscle. By 8 days post-fertilisation, approximately four rows of electrocytes have formed within the ventral fin fold, and the cell masses have significantly decreased in size [1]