430 F. H. Xrecker, 



States that four sucli groups are found on each side of the body in 

 Rhynchelmis of which the mid-ventral pair form the ventral nerve 

 cord and the remaining three the setae sacs and the lateral line nerve. 

 Iwanow pays little attention to these groups of cells in Lutnbriculus 

 except the ventral paii" from which he maintains that the nerve cord 

 is formed and v. Wagner in the sanie form described the nerve cord 

 as arising from this mid-ventral group of cells. The mid-ventral pair 

 of ectodermal enlargements is the only one I can distinguish and from 

 it the cells which form the nerve cord are derived (Fig. 15). Of course 

 the ectoderm cells are greatly enlarged elsewhere than on the ventral 

 side but any arrangement of the cells into groups was not observed 

 in Limnodrilus or Tubifex neither does v. Wagner see much evidence 

 of it in Lumhriculus. in addition to the "foundations" in the ecto- 

 derm Randolph describes a grouping of the neoblasts. She finds 

 four groups, originally, in Lumhriculus but by the fusion of the median 

 grou2)S these four are reduced to three; two lateral groups and one in 

 the medial line. Iwanow mentions only three groups in Lumhriculus 

 and in Limnodrilus and Tuhifex there seem to be only the three groups. 

 The median group evidently serves as a source of supply whereby the 

 two lateral groups which are 2iiore directly concerned in the formation 

 of new structures are replenished. 



The foregoing account of the part played by the neoblasts in the 

 course of normal regeneration at the ^Dosterior end of an individual has 

 shown that there is such a dose similarity between the neoblasts and 

 certain of the ectoderm cells as to cause considerable confusion and lead 

 to erroneous conclusions. A description of the changes in the ectoderm 

 during the absence of the intestine will show a still greater similarly, 

 than that thus far noted between these cells and the neoblasts. 



As mentioned in connection with the closure of the wound the 

 ectoderm meets over the aperture, becomes healed and presents an 

 unbroken surface. This is shown in Figure 2. Although the drawing 

 is made from a section at the level of the nerve it represents conditions 

 accurately for all levels so far as the ectoderm is concerned. It will 

 be noticed that the cells are not enlarged either near the nerve or in the 

 more central portion. Later the ectoderm begins to enlarge, not directly 

 opposite the nerve but somewhat dorsally, between it and the central 

 longitudinal axis of the body. Here the cells become columnar and 

 protrude beyond the surrounding cells both basally and distally. An 

 increase in size is also evident in the nucleus and the nucleolus (Fig. 18 

 and 13). The imcleus of the normal ectodermal cell is approximately 



