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5. The Regeneration of the Tail in Lumbriculus. 



By Harriet llandolph, Philadelphia, Pennsylvania. 



eingeg. 30. März 1891. 



An examination of the regeneration of Lumbriculus , made in the 

 biological laboratory of Bryn Mawr College. Pennsylvania and under- 

 taken with reference to a more special point , has led to results in re- 

 gard to the general mode of regeneration that differ materially from 

 those at present accepted. 



As some time must necessarily elapse before the complete account 

 can appear, I offer this preliminary paper for the sake of the bearing 

 of the results upon some biological questions. 



The researches of Bii low are the source of our knowledge in re- 

 gard to the regeneration of the tail in Lumbriculus, and for compari- 

 son they may be briefly summarized as follows: 



1 The processes of development in the regenerating tail are simi- 

 lar to those in the developing embryo. 



2) In the origin of the mesoderm alone is there a modification, 

 since the mesoderm is not as in the embryo given off from the ento- 

 derm, but arises in the regenerating tail from the line where ectoderm 

 and entoderm are continuous. 



The results of my work confirm Buio w's more general statement, 

 but differ most widely in regard to the origin of the mesoderm. They 

 are briefly: 



1) The new ectoderm arises by the proliferation of the ectoderm 

 around the line of fission. From the ectoderm is formed the ventral 

 nerve chain and the lateral nerve line. Between these two foundations 

 are two others on each side in positions corresponding to the subse- 

 quent positions of the nephridia and the ventral setae. I am not at 

 present prepared to say to what they give rise. From the ectoderm are 

 formed also the dorsal setae. 



2) The new entoderm is similarly formed from the old. When fission 

 occurs, the violent contraction of the longitudinal muscles curves the 

 body-wall inward and the wall of the alimentary canal outward so that 

 the two tend to meet and a union is ultimately established. A faster 

 growth of ectoderm than of entoderm furnishes the extent of material 

 necessary for the proctodaeal invagination. 



15) The new mesoderm is formed in great part from specialized 

 cells in the region of the peritonaeal epithelium of the ventral longi- 

 tudinal muscles, on each side of the ventral nerve cord between it and 

 the ventral row of setae. These cells, which I propose to call neo- 



