52 J. M. D. OLMSTED 



Probably if the worms had been fed they would have resumed 

 their usual form in a shorter time. At the time of collecting, 

 several worms were found in nature to possess regenerated 

 posterior portions, some having the parts perfectly restored, 

 others with the new part much too small for the rest of the body. 



Similarly, all missing lateral parts were restored after a longi- 

 tudinal cut which did not involve the cephalic ganglia. Diver- 

 ticula of the digestive tract could be seen in the new material 

 after ten days, and the original form was fairly well restored 

 after a month. It was noticeable that in all the cases of lateral 

 cuts in which a portion of the tail was removed there was a 

 tendency to form a tail regardless of the amount of material 

 available (cf. head-forming tendency inPlanaria maculata, Olm- 

 sted, '18). Longitudinal pieces always curved toward the cut 

 side, and there was always a greater accumulation of material at 

 the posterior end (figs. 3 and 4), often with the digestive tract 

 clearly differentiated within it. 



Restoration of material anterior to the cephalic ganglia was 

 complete in about ten days, though if some of the eye spots were 

 removed they were over two weeks in reappearing. 



The regenerative powers are, however, quite different when the 

 cephalic ganglia are injured, and each of the species followed the 

 poly clad rule for regeneration. Posterior pieces after a trans- 

 verse cut at any level of the body behind the brain were unable 

 to restore the missing anterior parts. One might imagine that 

 since anterior pieces can restore all the missing parts, posterior 

 pieces might be able to restore some tissue at least at the anterior 

 end, even if unable to regenerate a brain. But no matter where 

 the cut had been made, immediately behind the brain or at the 

 very tail, the raw edge was covered with epithelium and only a 

 very narrow white margin of new material extended beyond 

 the old tissue, even after a period of six weeks. Yet if the pos- 

 terior end of one of these headless pieces was removed, another 

 posterior end began to regenerate promptly and was completed 

 in only a slightly longer time than ordinary. Similarly, the 

 anterior tip of the head in front of the brain was unable to re- 

 generate at all. 



