THE ORIGIN, LOCATION, AND PROJECTIONS OF THE EMBRYONIC ABDOMINAL MOTOR-NEURONS OF DROSOPHILA

We have used a retrograde labeling technique to identify motorneurons for each of the 30 body wall muscles of an abdominal hemisegment in th e late stage 16 Drosophila embryo. Each motorneuron has a characterist ic cell body position, dendritic arborization, and axonal projection. In addition, we have determined the neuroblasts of origin for most of the motorneurons we describe. Some organizational principles for the n euromuscular system have become apparent: (1) There is no obvious topo graphic relationship between the cell body positions of motorneurons a nd the position or orientation of the muscles they innervate; (2) moto rneurons that innervate muscles of similar position and orientation ar e often clustered and have overlapping dendritic trees; (3) morphologi cally similar motorneurons are generally derived from a common neurobl ast and innervate operationally related muscles; and (4) neuroblasts c an give rise to more than one morphological type of motorneuron.