Regeneration in the African lungfish, Protopterus. II. Branching structures

Abstract

AbstractIt is possible to elicit the growth of a lateral branch from either the pectoral or the pelvic fin of the African lungfish Protopterus by excising a wedge of tissue, including cartilage, from the original limb. In pectoral limbs, 18 notches produced four bifids, but in pelvic limbs only one out of 14 cuts resulted in a branching element. Although cuts were distributed along the length of the limbs and along both anterior and posterior faces, accessory structures were elicited only from the posterior and posterior‐dorsal faces of the pectoral limb and from the anterior edge of the pelvic. The new branch was always of a size, proportion, and function nearly identical with that of the original, and to date none has grown longer than the equivalent branch of the primary limb. One broken pectoral limb gave rise spontaneously to a bifid growth.Fully developed horizontal branches effect changes in the long axis of the limb from which they have grown. Although the new filament first grows out perpendicular to the long axis of the primary element, it later assumes a shallower angle. Subsequent skewing of the axis of the primary limb results in a “Y” configuration. However, one vertically directed branch on the posteriordorsal surface of a pectoral limb, after ten months, still retains its original orientation, there having been no change in either its orientation or that of the original limb. One caudal anomaly is figured.