On Muscle Regeneration in the Limbs of Plethedon

The main changes that take place in the muscles of Plethedon cinereus during the process of regeneration are as follows: 1 (a) In the cut muscles the nuclei divide directly and in the outer bundles the fibers disintegrate, leaving masses of nuclei with a small amount of cytoplasm. (b) Some of the cells so formed later divide mitotically, and by them new muscle substance is laid down. (c.) As the number of nuclei is, however, far in excess of the normal number of muscle fibers, many nuclei must degenerate or be transported. 2. The fibers of the inner bundles do not disintegrate, but split longitudinally, giving rise to smaller fibers, which are soon indistinguishable from those formed as described in I. 3. The arrangement into muscle bundles first becomes clear at the end of about six weeks. 4. There is no change in the muscles of the upper arm. II. The following is a brief summary of the main observations that have been made on the power of regeneration of the limbs in European species of salamanders. Spallanzani (8), in 1768, published a number of observations on aquatic salamanders, presumably species of Triton. In these he found that any or all of the limbs will regenerate, no matter what the species, size, or age of the animal, the larger ones regenerating more slowly than the smaller forms. Regeneration will take place, he maintained, even when the limbs are disarticulated. Bonnet, 1777 (2), confirmed Spallanzani's observations, finding that in Triton cristatus the hands and fingers will regenerate. Von Siebold (7), in 1828, recorded abnormal regeneration of the fingers of Triton cristatus. Higginbottom, in 1847 (4, p. 29), observed that in Triton the limbs will regenerate at a temperature of from 48° to 57° F. Philippeaux (6), in 1866, was the first to prove conclusively that limbs when disarticulated will not regenerate. His experiments were made on Triton cristatus and Axolotl. Dumeril (3), in his paper of 1867, in the course of other observations, notes the fact that in an Axolotl the two anterior limbs regenerated after injury. Wiedersheim, 1875 (1, p. 95), found that the toes of Triton cristatus will regenerate, while there is no regeneration of the limbs in Proteus and Siren lacertina. Erber, 1876 (4, p. 34), notes regeneration of the feet of Siren lacertina. Goette, 1879 (5), records the regeneration of a leg of Proteus after a year and a half. Regeneration also occurs in Amphiuma and Siren, in Triton cristatus, T. taeniatus, and their larvae. Weismann (9), in The Germ Plasm, 1893, says that the limbs of Salamandra regenerate, while in Triton marmoratus regeneration is slight or absent. Barfurth (1), in 1894, reports regeneration of the feet and digits of Triton taeniatus and Siredon pisciformis. This regeneration is normal or abnormal according to the plane and method of the injury. I have experimented on the following forms, removing a fore foot and a hind foot from different individuals of each species: Plethedon cinereus, Spelerpes ruber, S. guttolineatus, Desmognathus ochrophaea, Manculus quadridigitatus, Amblystoma opacum, Diemyctylus viridescens, Amphiuma means, and Necturus maculatus. Of these, all have regenerated.1 The regeneration in Spelerpes, Desmognathus, Manculus, and Amblystoma was comparatively rapid, and new limbs were well formed in four months, though they were somewhat smaller than the old limbs. Diemyctylus was slower in reaction, while the first Necturus to show a distinct regenerated stump did so only after eight months. Other individuals of the same species showed no regeneration even at that time. I desire to thank Professor T. H. Morgan, under whose direction this work was undertaken, for his kindly assistance during its progress.