Cellular organization of a battery cell complex in Hydra. (a) Schematic representation showing the location of the different cell types in a battery cell complex. (Adapted from Figure 1e of ). (b, c) Double staining of tentacle tissue of Hydra magnipapillata with the monoclonal antibodies (b) NVl (neuron-specific, green) and (c) H22 (nematocyte-specific, red) shows innervation of the nematocytes (arrowheads indicate (b) the NV1+ nerve cell body and (c) four large nematocysts in different battery cells). (Reproduced from Figure 1a, b of ). (d, e) Staining of tentacle tissue with (d) NV1 monoclonal antibodies and (e) the CnAsh probe, which detects the product of achaete-scute, a gene specifically expressed in nematocytes and the sensory neurons of battery cells. (Reproduced from Figure 5 of ). Scale bar: 25 μm (b, c); 5 μm (e, d).