194 



REGENERA TION 



Lateral proliferations of ectoderm produce, according to some 

 writers, the material out of which the mesoderm of the new tail is 

 formed. Randolph, on the other hand, has described the new meso- 

 derm as arising from the old, especially from certain large peritoneal 

 cells that are found throughout the body. The cut-end of the diges- 

 tive tract closes, and later new cells develop at its posterior end. An 

 in-turning of ectoderm, in the form of a pit, fuses with the posterior .end 

 of the digestive tract and establishes communication with the outside. 



% 



B 



t: "..*'. 



FIG. 58. After Hescheler. Regeneration of anterior end of earthworm. A. After four days. 

 B. After eleven days. C. After twenty-five days. D. After twenty-one days (younger in- 

 dividual). 



The regeneration of the anterior end of the earthworm has been 

 carefully worked out by Hescheler, and although on account of the 

 greater complexity of the process the results are not so decisive as 

 those just described, yet in many respects they are in agreement. 

 In Hescheler's experiments only four or five anterior segments were 

 cut off. The closing of the cut-end is somewhat different from that 

 in lumbriculus. A plug of cells soon forms over the end (Fig. 



