Studies were performed on spherules of approximately $100-300 \mu$ in diameter obtained from the reaggregation of dissociated bulbar acoustic regions of 11-days incubation chick embryos. These spherules were cultured for 15 days and then prepared for electron microscope observations. We did ascertain that cellules of the nucleus magnocellularis are able to differentiate also in these in vitro conditions of anatomical and functional isolation and without any possibility of a root coclear fibers connection. Moreover, the cell body of these isolated cells displays specific synaptic connections with fibers that are certainly not root fibers, but with a typical calyciform model, as normally occurs for root coclear fibers only. We consider this finding a further experimental demonstration that it is the receiving neuron which determines the specific synaptic model, whatever the nature of the afferent axon. This property seems obviously acquired by the receiving neuron at the moment of the specific hystogenetic determination.