288 



LEONARD P. SAYLES. 



parently not involved. It is a rather common occurrence to 

 find one or two neoblasts on a septum in an uninjured worm so 

 that the few seen in these last segments are in accordance with 

 what is to be expected. In making these counts, not only 

 leucocytes, as suggested by Krecker ('23), but also nephridial 

 cells are apt to be mistaken for neoblasts in early stages of 

 metamorphosis. Cells of this type, as clearly demonstrated by 

 examination of adjacent sections, are shown in Fig. 9. Both 

 of these types of cells have quite large nuclei and nucleoli and 

 many nephridial cells are of course in contact with the septa. 



TABLE IX. 



NEOBLASTS. 



On the four or five septa nearest the wound, therefore, neo- 

 blasts are most abundant, as also observed by Krecker ('23). 

 About nine segments in all, however, seem to be involved while 

 Krecker reports the maximum distance as seven. The region 

 involved in the production of neoblasts is, therefore, approxi- 

 mately the same as that in which cell proliferation occurs in 



the intestine. 



Ectoderm. 



The ectoderm, unlike the other two types of tissue already 

 discussed, regenerates solely from cells in the immediate vicinity 

 of the wound. That cells from the old hypodermis form the 

 new hypodermis and nerve cord is generally agreed upon. 

 Krecker ('10, p. 430) describes the marked enlargement of certain 

 ectoderm cells "not directly opposite the nerve but somewhat 

 dorsally, between it and the central longitudinal axis of the 

 body." These cells increase in size and become so changed 

 that, as he expresses it (p. 434), "were these cells seen alone they 

 would be immediately considered neoblasts." Of the changes 

 which take place in cells other than those of this particular 

 region, however, he makes no more than the simple statement 

 (p. 430) that "of course the ectoderm cells are greatly enlarged 

 elsewhere than on the ventral side." 



