392 BIOLOGY: GENERAL AND MEDICAL 



Other descriptive terms used by Morgan are Epi- 

 morphosis, in which a proliferation of new material pre- 

 cedes the development of the new part, and Morpha- 

 laxis, in which a part is transformed directly into a new 

 organism or part of an organism without proliferation at 

 the cut surfaces. 



So far as is known, the first observations upon the 

 regeneration of lost parts was made by Bonnet, who, in 

 1741, experimented with earth-worms. When he cut 

 a common earth-worm in half, the anterior half grew new 

 segments, forming a new tail, and the posterior half 

 new segments and a new head, so that eventually two 

 entire worms resulted. The regenerative capacity was 

 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 



