the hairs encode information about strength and location of a stimulus via timing differences in firing. Platypuses In contrast to the sinus hairs that other mammals use to detect water movements, evidence indicates that platypuses use specialized mechanoreceptors on the bill called “push-rods”. These look like small domes on the surface, which are the ends of rods that are attached at the base but can move freely otherwise. Using these push-rods in combination with electroreceptors, also on the bill, allows the platypus to find prey with its eyes closed. While researchers initially believed that the push-rods could only function when something is in contact with the bill (implicating their use for a tactile sense), it is now believed that they can also be used at a distance to detect hydrodynamic stimuli. The information from push-rods and electroreceptors combine in the somatosensory cortex in a structure with stripes similar to the ocular dominance columns for vision. In the third layer of this structure, sensory inputs from push-rods and electroreceptors may combine so that the platypus can use the time difference between arrival of each type of signal at the bill (with hydrodynamic stimuli arriving after electrical signals) to determine the location of prey. That is, different cortical neurons could encode the delay between detection of electrical and hydrodynamic stimuli. However, a specific neural mechanism for this is not yet known. Other mammals The family Talpidae includes the moles, shrew moles, and desmans. Most members of this family have Eimer's organs, touch-sensitive structures on the snout. The desmans are semi-aquatic and have small sensory hairs that have been compared to the neuromasts of the lateral line. These hairs are termed “microvibrissae” due to their small size, ranging from 100 to 200 micrometers. They are located with the Eimer's organs on the snout and might sense water movements. Soricidae, a sister family of Talpidae, contains the American water shrew. This animal can obtain prey during the night despite the darkness. To discover how this is possible, a study controlling for use of electroreception, sonar, or echolocation showed that this water shrew is capable of detecting water disturbances made by potential prey. This species probably uses its vibrissae for hydrodynamic (and tactile) sensing based on behavioral observations and their large cortical representation. While not well studied, the Rakali (Australian water rat) may also be able to detect water movements with its vibrissae as these