Motility in chick embryos with substitution of lumbosacral by brachial by lumbosacral spinal cord segments

In two and one‐half‐day chick embryos, brachial segments were substituted for lumbosacral segments (Bl series) and vice versa (Lb series). Recordings were made of spontaneous (type I) motility in 9‐ to 17‐day embryos at daily intervals. Total embryonic motility (per cent time spent in activity in 10‐minute periods) and total wing and leg motility did not differ significantly from normal in both series. Furthermore, frequency of movements (per minute) was recorded for wings and legs separately and for combined wing/leg movements. In both experimental series, combined wing/leg movements were significantly more frequent and isolated wing or leg movements less frequent than in normal embryos. This means that two brachial or two lumbosacral segments in the experimental embryos are more tightly coupled than the brachial and lumbosacral segments in a normal embryo. Regional differences between brachial and lumbosacral segments are thus demostrable as early as nine days. The increased frequency of combined wing/leg movements persists after hatching. In hatched chicks of the Bl series, legs are incapable of making alternating stepping movements; they are always abducted and adducted simultaneously as in wing flapping. This is another expression of regional specificity of the brachial cord. We assume that regional specifications of spinal cord segments are built into the cord at the stage of operation.