Formation of the receptor system in the hind limb of the locust embryo.

The formation of the peripheral nervous system in the metathoracic limb bud of a locust embryo was studied by antibody [anti-(horseradish peroxidase); (anti-HRP)] labelling. At 50% of embryogenesis, the major neural routes from the periphery to the CNS are established. There are two waves of receptor cell genesis, (a) At about 35%, the first precursors of internal receptors emerge from the epidermal cell layer and at about 58% apparently all internal receptors are formed. At this stage, the number and arrangement coincide with those of the first larval instar, (b) At the 55% stage, anti-HRP-immunoreactive cells appear, which can be associated with exteroceptors (hairs, campaniform sensilla); these reach their final number and cellular constitution at 65%-70% embryogenesis. The two waves are correlated to the formation of the first and second embryonic cuticle. The results thus indicate that the genesis of the receptor system and its connections to the CNS is completed at about 2/3 of embryonic development.