230 



COLLEGE ZOOLOGY 



stimulation, in which condition slight stimuli cause violent 

 responses. 



Regeneration and Grafting. Earthworms have considerable 

 powers of regeneration and grafting (p. 117). Some of the results 

 of experiments along this line are shown in Figure 160. A 

 posterior piece may regenerate a head of five segments (A) or 

 in certain cases a tail (B). Such a double- tailed worm slowly 

 starves to death. An anterior piece regenerates a tail (C). 



Three pieces from several worms may 

 be united so as to make a long 

 worm (D) ; two pieces may fuse, 



\J 



A B 



FIG. 1 60. Regeneration and grafting in the earthworm. A, head end of 

 five segments regenerated from the posterior piece of a worm. B, tail re- 

 generated from the posterior piece of a worm. C, tail regenerated from an 

 anterior piece of a worm. D, union of three pieces to make a long worm. 

 E, union of two pieces to make a double-tailed worm. F, anterior and pos- 

 terior pieces united to make a short worm. The dotted portion represents 

 regenerated material. (From Morgan.) 



forming a worm with two tails (E) ; and an anterior piece may 

 be united with a posterior piece to make a short worm (F). 

 In all these experiments the parts were held together by threads 

 until they became united. 



Economic Importance. Charles Darwin in his book on the 

 Formation of Vegetable Mold through the Action of Worms has 

 shown by careful observations extending over a period of forty 

 years how great is the economic importance of earthworms. 

 One acre of ground may contain over fifty thousand earthworms. 



