AN EXPERIMENTAL DEMONSTRATION OF THE REGENERATION OF THE PHARYNX OF ALLOLOBOPHORA FROM ENDODERM

Abstract

SEVERAL recent investigators have shown with more or less probability that the lining of the new pharynx which develops during the regeneration of the head in certain earthworms comes from the endoderm, while the pharynx of the embryo is lined by ectoderm.' It seemed that by means of experimental methods this relation might be definitely determined. In the following pages I shall describe some experiments on Allolo bophora foetida that demonstrate, I think, that the lining of the new pharynx is in fact derived from the endoderm. Hescheler showed, as the result of observations made prin cipally on Allolobophora terrestris, that when the five anterior segments are cut off the pharynx is regenerated by a growing forward of the old digestive tract up to the third segment, and that the new buccal cavity occupying the first three segments is formed by an ectodermal invagination. The old pharynx was not completely removed in these operations, since in the normal worm its cavity frequently extends beyond the fifth segment and its thickened muscular dorsal wall always goes back into the sixth, so that Hescheler's results are open to the objection that in his experiments apart, at least, of the old pliaryngeal wall always remained behind as a possible source for the regeneration of the new pharynx. Rievel in experimenting on certain Lumbricidae (Allolobo phora foetida, Allolobophora terrestris, Lumbricus rubellus) cut off anterior ends consisting of between one-third to two thirds of the entire body. He arrives at the conclusion that the pharynx is regenerated from the walls of the digestive tract