446 T. H. MORGAN. 



indebted to Miss Elizabeth Nichols^ Fellow in Biology, Bryn 

 Mawr College, who began this study of regeneration with me. 

 Many of the early experiments were largely carried out by her ; 

 and later, when the work devolved on me, I profited much by 

 the results of the previous work. 



There were several main problems that I wished to work 

 out. First, the extent to which the earthworm could regene- 

 rate; secondly, the number of new segments that would reap- 

 pear in the anterior end after the removal of a definite number; 

 thirdly, the presence or absence of abnormalities in the re- 

 generated anterior segments. 



Certain rough results were at first obtained, which showed 

 that when many segments were cut ofi" only a few segments 

 replaced them. That is to say, there was no apparent connec- 

 tion between the number of segments that were cut off and the 

 number that regenerated. Four and rarely five new segments 

 came back. 



I then set to work to determine what result would follow 

 when only a few segments were cut off, for obviously if four 

 came back when one, two, or three were cut off, the result 

 would appear as though the reproductive organs had all shifted 

 posteriorly. The tables below that are first given show the 

 results of these latter experiments. 



One of the most conspicuous results was the great decrease 

 in size that the worms suff'er during the period of regeneration. 

 When only a few segments were cut oflF the regeneration was 

 soon accomplished, and no great decrease in the size of the 

 body of the worm was obvious ; but where many segments 

 were cut ofi', and regeneration only took place after several 

 months, or not at all, the body dwindled until it got to be less 

 than a half of its original size. I have not made a histological 

 study of these worms to determine what organs have suflFered 

 most during the period. 



The worms used wereL.(or AUolobophora) foetid us, which 

 live in manure heaps. They were kept in ordinary flower-pots 

 filled with the manure in which the worms were found living. 

 The pots stood in about an inch of water, and each was covered 



