Pattern regulation of mesoderm in transplanted and supernumerary limbs of the cockroach. I. The final morphology

Muscles, nerves, and tracheae were examined histologically in clusters of three limbs arising from single mesothoracic leg sockets in the cockroach, Periplaneta americana. The three‐limbed preparations were produced by amputating a normal legand replacing it with a contralateral leg from a donor animal, with the anterior‐posterior (A‐P) axis of the graft reversed relative to the A‐P axis of the host. After a few molts, two supernumerary limbs develop from the host/graft junction, one anterior and one posterior to the graft. Three to nine months after the operation, femurs from the supernumerary and graft limbs possess identifiable muscles which are, however, not as well developed as those of normal limbs. Supernumerary coxae rarely possessidentifiable musculature, but distal regions of the transplant coxae contain muscles of nearly normal morphology. Near the host/graft junction, the coxal muscles are disorganized, producing a proximal to distal gradient in muscle organization within thecoxa. The extensive disorganization near the host/graft junction is primarily a result of the reversed axis, since in grafts of ipsilateral limbs without axis reversal, there is considerably less muscle disorganization near the host/graft junction. Large, nerves and large tracheae were often located in supernumerary and graft femurs and in graft coxae in approximately the same positions as in normal limbs.