AN EXPERIMENTAL DEMONSTRATION OF THE 



REGENERATION OF THE PHARYNX OF 



ALLOLOBOPHORA FROM ENDODERM. 



JOHANNA KROEBER. 



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 



o o 



comes from the endoderm, while the pharynx of the embryo is 

 lined by ectoderm. 1 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 a part, at least, of the old 

 pharyngeal zvall ahvays 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 



1 See Hoffman, Zeit.f. wiss. Zool. Bd. Ixvi. 1899. 



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