Foetal sense organ. Coloured scanning electron micrograph (SEM) of a section through a foetal olfactory (smelling) sense organ known as the vomeronasal organ (VNO), or Jacobson's organ. The vomeronasal organ is found in the nasal septum and is mainly used to detect pheromones, which are chemical messengers that carry information between individuals of the same species. Magnification: x250 when printed 10 centimetres wide.