376 BIOLOGY: GENERAL AND MEDICAL 



not, however, so restricted, for he also found that if he 

 cut the worm into three, four, eight, ten, or even fourteen 

 pieces, each piece eventually reproduced the lost seg- 

 ments, including the head and the tail, so that as many 

 complete worms resulted as he had fragments of the 

 original worm. " The growth of the new head is limited 

 in all cases to the formation of a few segments, but 

 the new tail continues to grow longer, new segments 

 being intercalated just in front of the end piece which 

 contains the anal opening." " Bonnet found that if a 

 newly regenerated head is cut off, a new one regenerates, 

 and if the second one is removed, a third new one de- 

 velops, and in one case this occurred eight times; the ninth 

 time only a budlike outgrowth was formed." "In other 

 cases a new head was produced a few more times, but 

 never more than twelve times." Short pieces removed 

 from either end of the worm failed to regenerate, but 

 died after a few days. Sometimes two new heads or 

 two new tails regenerated. The polarity of the organ- 

 ism was always preserved; i.e., the heads always grew 

 at the anterior, never at the posterior, end. 



These results of Bonnet have been confirmed again 

 and again. The regenerated head is perfect, including 

 the oral opening, the oesophagus, and the brain. 



Morgan found that when the head of the worm known 

 as Allolobophora fcetida was amputated, its regeneration 

 was always perfect; that is, if one, two, three, four, or 

 five segments are removed, exactly the same number 

 were renewed. If, however, six or more were removed, 

 only four or five are regenerated, so that the head is 

 perfected, but the full number of segments behind the 

 head is never reproduced. He found this to be the rule 

 for all the annelids. With regard to the posterior end, 

 he found that when it was amputated, the terminal end 

 contained the new opening of the alimentary canal and 

 that the new segments, of which the full complement 

 always forms, arise in front of this terminal segment, the 

 youngest always being the one immediately in front of it. 



