The history of the case in which a limb of original prospective asymmetry developed is given on page 126. In this individual the limb bud, as it began to grow, pointed anteriorly (fig. 63), and continued to grow in that direction. Though it remained small and imperfect (fig. 64), it is clearly a right limb on the left side (not reversed).

The cases which formed reduplications began their development in the same manner. The first direction of pointing is recorded as anterior in nine cases, anterodorsal in eight, and anterolateral in five. Three are described as pointing dorsally and one laterally. Thus these limbs all show in greater or less degree the initial effect of their original growth tendency. Growth of the bud continues then for some days in a general anterior direction, but sooner or later a reduplicating bud appears, usually at the posterior border of the original bud, and this grows in most cases into an appendage equal to or exceeding the original in size. If the reduplicating bud does not appear until late, then the original one may attain considerable size and remain, for some time at least, the principal member (figs. 65 and 66). If it appears earlier, but not until the original bud has a good start, then the two members may remain of almost equal size (figs. 67 to 71). In other cases, where the reduplicating bud begins to grow early, it soon gains the upper hand, and the original may be reduced to an atrophic or rudimentary limb (figs. 72 to 74). This condition leads over to the single reversed appendage in which the original bud is reduced to a spur or nodule

Figs. 63 and 64 Orthotopic transplantation; right limb bud to left side (het.dd.). Exp. R. E. 87. Resulting limb, though defective, is reversed. N, normal right limb; TR, transplanted limb. X 10.

Fig. 63 Dorsal view, seven days after operation.

Fig. 64 Ventral view of specimen preserved sixteen days after operation. Figs. 65 and 66 Orthotopic transplantation; right limb to left side (het.dd.). Exp. R. E. 96 Resulting limb reduplicated.

Fig. 65 Ventral view, ten days after operation; primary limb (PR) points into gills; reduplicating bud (DU), just appearing. X 10.

Fig. 66 Ventral view, nineteen days after operation; primary member (PR) shows evidence of reduplication of hand; reduplicating member (DU) is in approximately normal position. X 10.

51 R. E. 87.

(p. 49). The reduplicating limb is, of course, mirrored from the original and hence corresponds to the side of the body on which it is grafted.

Being placed in the position of the normal limb, the reduplication is favorably situated with regard to blood and nerve supply, and it is probably on this account that so many of them develop into functional appendages. In this respect the experiments of this group differ considerably from the preceding (homopleural inverted), where there is a greater tendency for the original member to retain its predominant condition. Otherwise the course of development in the two groups is strikingly alike.

For the study of the details of reduplication, nineteen cases are available, including one case with small wound not considered in the table. Seven others were preserved at relatively early stages in order to investigate the internal processes involved. Histories of several typical cases are given in the appendix.

Seventeen of the cases conform to the main type and do not differ materially from those considered in the last section. As in the homopleural inverted limbs (p. 35), the degree and character of the reduplication vary much from case to case. In some the digits alone are doubled, and at the other extreme we find two almost entirely separate limbs. In thirteen individuals a second reduplicating limb formed on the anterior side of the original. These usually did not develop so completely as the limbs arising from the posterior buds, and the reduplication often involved only the distal part of the manus, with the digits more or less symmetrically placed. The anterior reduplications are mirrored from the ulnar or ulnopalmar surface and occasionally from the

Figs. 67 to 70 Orthotopic transplantation; right limb to left side (het.dd.). Exp. R. E. 70. Resulting limb reduplicated. N, normal right limb bud; TR, transplanted limb bud; PR, primary member; DU, reduplicating member. X 10. Fig.67 Dorsal view, five days after operation. The transplanted bud already gives evidence of reduplication.

Fig. 68 Dorsal view, ten days after operation. Reduplicating bud is large and in normal position.

Fig. 69 Dorsal view, sixteen days after operation.

Fig. 70

Dorsal view of specimen preserved thirty days after operation. Fig. 71 Similar case (Exp. R. E. 71); ventral view, twenty-two days after operation. X 10.

palm. One case52 had three almost complete separate appendages (figs. 75 and 76).

Two cases of the nineteen gave rise to an anterior reduplicating bud only, which in both individuals was mirrored from the ulnopalmar surface. Owing to the position of the reduplicating bud in front of the original heteropleural limb, it could not be brought into normal posture (fig. 77).

There remain to be considered the five cases in which the asymmetry of the transplanted bud was reversed. These are of the utmost interest in showing how a secondary factor (reduplication) may so modify the result that the rules of symmetry seem not to hold. They show more than any others the necessity of having complete histories in each case, for the manner in which the end result is reached is of cardinal importance for the correct interpretation of the process. As stated above, these cases gradate into those in which duplicate limbs arise, so that the classification is somewhat arbitrary, the single-limb condition being a masked reduplication. Like the others, they begin their development with growth of the bud in an anterior direction (figs. 83 and 86). Then a posterior reduplicating bud makes its appearance, and the original bud is rapidly reduced (figs. 84 and 85 and 87 to 89) in relative importance, becoming a spur or nodule attached to the latter. The history of a typical case is given on page 128.

Figs. 72 to 74 Orthotopic transplantation; right limb bud to left side (het.dd.). Exp. R. E. 74. Reduplication with atrophic primary member. N, normal right limb; PR, primary transplanted limb; DU, reduplicating member. X 10.

Fig. 72 Dorsal view, twelve days after operation; the primary limb already appears as an appendage of the reduplicating member.

Fig. 73 Ventral view, twenty-one days after operation.

Fig. 74 Lateral view of transplanted limb.

Fig. 74A Dorsal view of same.

Figs. 75 and 76 Orthotopic transplantation; right limb bud to left side (het. dd.). Exp. R. E. 133. Two almost perfect reduplicating members, one anterior (A.DU) and one posterior (P.DU) to the primary (PR). The relations of these limbs are just as in the diagram, fig. 4B. X 10.

Fig. 75 Ventral view, eleven days after operation.

Fig. 76 Ventral view, nineteen days after operation. B, lateral view of posterior reduplicating member.