No. 3] THE TAIL IN LUMBRICULUS. 319 



in optical section, as has already been pointed out by Kleinen- 

 berg (11), is the result of the invagination of the new procto- 

 deum, and of the fact that the anal opening is situated at first 

 somewhat dorsally. If, therefore, the new mesoderm arises 

 from this point, it is ectodermic in origin ; but in my view it is 

 to be considered as arising from elements in the old mesoderm. 



Other important results reached by Biilow are as follows : — 



"3. Der centrale Theil des Bauchnervensystems, dessgleichen 

 die Spinalganglien entstehen aus einer paarigen Ektoderman- 

 lage ; es kommen zu dem nervosen Theil des Bauchnerven- 

 stranges von Lumbriculus keine mesodermalen Elemente hinzu, 

 wie Semper dies fiir die Naiden angiebt." 



With this my results are in perfect agreement. 



" 5. Die Chordazellen Semper's sind Abkommlinge des mitt- 

 leren Keimblattes ; sie verschwinden dort wo die Anlage des 

 * Neurochords ' beginnt." 



My observations confirm the first part of this statement, but 

 show that the so-called Chorda cells persist in every segment 

 except the most anterior of the adult worm. For these cells I 

 have proposed in a preliminary paper (16) the name Neoblasts. 



"6. Die Muskelplatten und die sonstigen muskulosen Ele- 

 mente sind mesodermalen Ursprungs, dessgleichen Segmental- 

 organe, ' Leberzellen ' und Blutgefasssystem." 



In regard to the nephridia, I do not find that the mesoderm 

 alone takes part in their formation, although I am unable to 

 decide exactly how much arises from the ectoderm. The ma- 

 terial seems to me unfavorable for a determination of the ques- 

 tion ; and as among a number of forms examined Lumbriculus 

 gives the clearest picture of regeneration, the matter must prob- 

 ably be decided by analogy from the embryology of this or of 

 an allied form. All the processes of development are less dis- 

 tinct in the regenerated tail than in the embryo, in consequence 

 of the reduced size of the cells and the relatively smaller space 

 that they occupy. It is then perhaps not remarkable that some 

 details of the development of the regenerated tissue cannot be 

 elucidated. 



On account of the more normal aspect of its tissues Lumbri- 

 culus is more suitable for a study of the phenomena of regen- 

 eration than any other form that I have examined. My first 

 investigation of this subject was made upon Lumbricus ; but 



