532 C. M. Child. 



would probably, if exposed, not produce anything like complete 

 anterior regeneration except in the presence of the cephalic ganglia. 

 It is of course possible that differences between L. atomata and 

 L. tremellaris may exist; for example, in the former the produc- 

 tion of new tissue at the anterior end in the absence of the cephalic 

 ganglia may be so slow that union ot the sides of the cut occurs 

 before its amount is appreciable, while in the latter sufficient new 

 tissue is formed to prevent complete union of the old cut edges. 

 It is extremely improbable, however, that regeneration of the 

 region anterior to the cephalic ganglia does not occur. Even in 

 the rhabdococla, most of which have little power of regeneration, 

 the preganglionic region is regenerated rapidly and completely. 

 The experiments already described are, I think, sufficient to show 

 that no such simple explanation as that of Schultz's will suffice 

 for L. tremellaris. Certain other experiments which I performed 

 with this particular purpose in view may be described since they 

 afford some facts of interest. 



In these experiments posterior pieces from various levels were 

 employed, but chiefly those from the pharyngeal region, since 

 contraction of the cut surface is most marked here (see Figs. 38 

 and 39). After section such pieces were allowed to remain un- 

 disturbed during several days in order that the cut surface might 

 be contracted as much as possible. Then they were subjected 

 to a second operation, in which the lateral regions which had 

 been drawn toward the median plane by the contraction were 

 removed. 



Two series of this kind from different levels are described; these 

 were begun at the same time and examined at the same intervals 

 and so are available for comparison as to the amount of regenera- 

 tion at different levels after a second operation. 



Series 75. Five posterior pieces were obtained by cuts just 

 anterior to the anterior end of the pharynx. 



Eight days after section all were either like Fig. 44 or somewhat 

 more widely open, the space being filled with new tissue. All 

 were cut in the manner indicated in Fig. 44. Contraction after 

 this second operation was comparatively slight and the anterior 

 cut surface remained widely open in every case. The condition 



