Permeability of tarsal sensilla in the tick Amblyomma americanum L. (Acarina, Ixodidae)

Ticks were submerged in silver-protein solution, prior to fixation for electron microscopy, in order to trace the pathway of molecules in supposed tarsal chemoreceptors. Sensilla with radially arranged cuticular canals (100-200 A in diameter) leading to the centrally located dendrites show silver granules inside the canals and in the central lumen, thus directly making contact with the dendrites. Sensilla with large, plugged pores (1200 A) exhibit an accumulation of silver granules in the pore openings but no granules (about 50 A in diameter) were observed penetrating into the lumen. Apparently silver granules could diffuse in, but not through the material which suspends the pore plugs. It is suggested that this material corresponds to the 'pore tubules' in insect olfactory sensilla and that it may play an essential role in transmitting a chemical stimulus from the environment to the dendrites.