Heteromorphic Tail in Allolohophora. 351 



Since there were but few worms cut further back than the eigh- 

 teenth segment, and since the stomach-intestine begins at this level, 

 all the observations made on worms cut posteriorly to the eigh- 

 teenth segment were brought into one class. It is worth noting, 

 however, that of the four heads regenerating at these levels, three 

 formed from worms cut at the nineteenth segment, while the 

 fourth formed from a worm in which the exact level of the cut 

 was not noted. The percentages In the different classes, though 

 based on a small number of cases, yet bring out clearly one or two 

 points. When a worm was cut in two In front of the stomach- 

 intestine, In no case was a heteromorphic tail formed. The per- 

 centage of cases In which a head was formed grows less as the sec- 

 tion Is made further back on the worm, the fall of percentage 

 being very great Immediately behind the gizzard. This tends to 

 support the hypothesis that the formation of a heteromorphic tail 

 is favored by the presence of the stomach-intestine near the cut 

 end, though when the section is not more than one segment back 

 of the gizzard a head is sometimes formed. 



Though the preceding experiments seem to show that the devel- 

 opment of a heteromorphic tail is connected with internal struc- 

 tures in the worm, they leave untouched the question of the kind 

 of regeneration that takes place from posterior ends of anterior 

 pieces cut anterior to the stomach-intestine. This point should be 

 determined, and I hope In the future to undertake a set of experi- 

 ments in which the posterior regeneration from anterior pieces 

 will be observed. 



