A STUDY OF METAMERISM. 423 



These measurements show conclusively that tlie greater 

 number of new abnormalities occur not more frequently at the 

 beginning of the newly formed portion than throughout all the 

 later period of growth. 



Summary. — In the 40 cases mentioned above 4 were not 

 well enough developed to furnish any data. In the 36 that remain 

 there were only two that did not show any abnormality, and it 

 is noticeable that each of these had only formed at the time a 

 few new segments (six each). We must conclude from the 

 data that about 18 worms out of every 19 would show abnor- 

 malities in the regenerated posterior end. 



In these same worms the number of abnormalities in the 

 region of the body anterior to the regenerated end was recorded. 

 This gives us data to show whether the irregularities are due to 

 inherited peculiarities of the tissue or to the conditions acting 

 during regeneration. In the 12 cases recorded in c 9 were 

 normal in front of the regenerated portion^ and 3 showed ab- 

 normalities, — that is, as 1 to 3. In the 6 cases recorded in d, 5 

 were normal in front and 1 abnormal (1 to 5). 



In the 4 cases in e there were no abnormalities in front. In 

 the 12 cases recorded in f there were 2 cases unrecordedj and 

 the remaining 10 had no abnormalities in front. 



To sum up, the evidence points unmistakably to the con- 

 clusion that the abnormalities found so frequently in regene- 

 rated portions are due to the conditions acting during regene- 

 tion (from within or from without), and in no way connected 

 with an hereditary tendency to be more abnormal in one case 

 than in another. That is to say, the tissues of a worm that has 

 developed normally from the egg are just as apt to develop 

 irregularly in regenerating as are the tissues that have de- 

 veloped irregularities during embryonic growth. Heredity 

 seems to have nothing to do with causing the abnormalities. 

 In fact, one might say that the tissues inherit a strong tendency 

 to regenerate normal metameres, but the means at command 

 are so imperfect that abnormal results are frequent. 



Will the large proportion of abnormalities present in regene- 

 rated worms, taken in connection with the number of worms found 



VOL. 37, PART 4. NEW SER. p P 



