A Motorneurone Cell Body Located Either Dorsally or Ventrally within a Crustacean Abdominal Ganglion

In the last abdominal ganglion of the squat lobster Galathea strigosa (Decapoda, Anomura) a unique pair of flexor motorneurones exist whose medial cell bodies occur paired either on the ventral or the dorsal surface of the ganglion or else are located separately, one dorsal and the other ventral. In 60 squat lobsters (30 ♂ 30 ♀), this pair of medial dorsal/ventral (MDV) cell bodies was found in 4 distinct cell pair configurations: ventral/ventral, 24; dorsal/dorsal, 5; right ventral/left dorsal, 14; right dorsal/left ventral, 17. MDV cell bodies were never found lying midway between the dorsal and ventral surfaces. The distribution of configurations was approximately the same for both sides of the ganglion and for both sexes, and whether a cell occurred ventrally or dorsally was found to be independent of the position of its partner. The determination of cell body location appears not to be influenced by any cell‐cell interaction, despite an apparent ‘point of close association’ between the two soma neurites and a strong bias overall towards the ventral location (dorsal 1/3, ventral 2/3). 1987 The Royal Swedish Academy of Sciences