...to investigate the basic biophysical mechanisms enabling the animals to sense the required cues in their environment. The aim of this project is to identify a structural candidate for a putative magnetite-based magnetoreceptor in sensory nerve endings of the ophthalmic branch of the trigeminal nerve in fishes und birds. For this purpose, we will use light-microscopy combined with spatially resolved magnetometry to detect magnetic particles in neuronally labelled tissue slices and electron microscopy to reveal their ultrastructure.