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THE AMERICAN NATURALIST [Vol. XLIX 



the curve shown in Fig. 1 were secured from worms which 

 regenerated in the fresh-water, as well as from those 

 which regenerated in the salt-water, environment. The 

 above observations make it seem probable, therefore, that 

 the form of the curve does not differ fundamentally from 

 the form which it would have had if all the worms had 

 regenerated in salt-water surroundings. 



In. Fig. 2 is shown the normal appearance of the ven- 

 tral aspect of the posterior end of a worm in which there 

 has been no regeneration. It will be noticed that the 

 length of the segments gradually decreases toward the 

 posterior end; but in Fig. 3, which is a camera lucida. 

 drawing of the posterior portion of one of the regen- 

 erated worms, the length of the segments decreases ab- 

 ruptly at the point X, showing that to be the point at 

 which the tail was removed. 



Three worms from which eight posterior segments were 

 removed regenerated double tails. Morgan ('97) and 

 Michel ('98) observed the same phenomena in Allolobo- 

 phora fcetida. One of these worms is shown in Fig. 4. 



Some attempts were made to determine the rate of 

 regeneration anteriorly at different levels on the worm's 

 body. At present all that can be said is that regeneration 

 posteriorly takes place much more frequently and rapidly 

 than anteriorly. 



The conclusions that follow from these experiments are: 



1. Enchytraus albidus regenerates posteriorly when 

 cut off at any level between eight segments from the pos- 

 terior end of the body and eight segments from the an- 

 terior end. It will be noticed that although the mortality 

 in pieces containing only the eight most anterior segments 

 was about 94 per cent., yet those that did survive regen- 

 erated from three to eleven (on the average seven) seg- 

 ments. In other words, a piece from the extreme anterior 

 end, containing only one eighth the number of segments 

 in the whole worm, can regenerate nearly as many seg- 

 ments, on the average, as it had at the beginning of the 

 experiment. Morgan ('97) found that in Allolobophora 



