The prosoma is formed in the embryo by fusion of the ocular somite (referred as "acron" in previous literatures), which carries the eyes and labrum, with six post-ocular segments (somite 1 to 6), which all have paired appendages. It was previously thought that chelicerates had lost the antennae-bearing somite 1, but later investigations reveal that it retain and correspond to a pair of chelicerae or chelifores, small appendages that often form pincers. somite 2 has a pair of pedipalps that in most sub-groups perform sensory functions, while the remaining four cephalothorax segments (somite 4 to 6) have pairs of legs. In primitive forms the ocular somite has a pair of compound eyes on the sides and four pigment-cup ocelli ("little eyes") in the middle. The mouth is between somite 1 and 2 (chelicerae and pedipalps).