Abstract
Experiments with the hind limb of Amblystoma punctatum were undertaken to compare its developmental behavior with that of the fore limb, as described by Harrison. 1
In normal development the hind limb does not appear as a definite bud until approximately 2y2 weeks later than the fore limb, so that it lies latent in the host for a much longer period after transplantation than does the fore limb bud. Furthermore, the 2 halves of the pelvic girdle are intimately fused in the median line, while the corresponding halves of the pectoral girdle are separate.
A preliminary experiment was done to determine the location of the hind limb rudiment at the stages used for operation. During the tail bud stage it was found that it lies ventral to myotomes 16, 17 and 18. The posterior rounded part of the body wall is its approximate caudal limit.
The following experiments were performed to test the equipotentiality of the hind limb. The limb rudiment was removed and the wound allowed to heal without covering. In this case a complete limb and girdle developed from the surrounding tissue. The same result followed when only a part of the rudiment was removed and the wound left uncovered. When the limb rudiment was extirpated and the area blocked with indifferent ectoderm, no limb developed, and the pelvic girdle was absent. When all, or a sufficiently large part of the hind limb rudiment was transplanted to an abnormal location, such as the flank, a complete limb and girdle developed at the site of implantation.
Hence, the hind limb of Amblystoma constitutes a harmonic equipotential system, just as Harrison found to be the case with the fore limb. 2 The pelvic girdle, however, differs from the pectoral girdle in that it also constitutes a harmonic equipotential system, while the girdle of the fore limb has been shown by Detwiler to be a mosaic system. 3
Get full access to this article
View all access options for this article.