Fig. 1. Structure of subesophageal ganglion (SubEG) from embryonic and juvenile leeches. (A) SubEG and first midbody ganglion from a juvenile leech. Surrounding tissue was removed to reveal the structure, and connections with the supraesophageal ganglion were severed. (B) SubEG in embryo at 47% of embryonic development (% ED; Reynolds et al., 1998b), which is about the stage at which we performed surgeries. The ganglionic precursors to each of the neuromeres are still separate at this stage. (C) The head of an embryo at 50% ED (ventral view) following ablation of presumptive neuromeres 1 and 2. (D) SubEG of juvenile leech in which neuromeres 1 and 2 were ablated at 50% ED.