No. .><>«> j 



EEGENEBATION 



291 



scribed above the animal did not begin to orient itself 

 with respect to the source of light until about the twelfth 

 day, but in another case the response took place on the 

 second day, which shows that this reaction does not de- 

 pend upon the central nervous system. It should be 

 stated that normal Throne similarly placed were used as 

 controls. Thyone A was quite sensitive to shadows and 

 to touch on the ninth day, but it reacted more quickly on 

 the twenty-fourth day both to shadows and to mechanical 

 disturbances. Whether this was due to the regeneration 

 of a new central nervous system, or to a more highly 

 developed specialization of function in the old tissue, I 

 am unable to say. It is quite possible that both factors 

 were involved. Eespiration is undoubtedly correlated 

 with the activity of the animal, and feeding movements 

 do not occur until the regeneration of all organs is well 

 ♦■'stablished, at about twenty-seven or twenty eight days. 



The internal changes that take place during regenera- 

 tion were studied in animals that were killed at different 

 stages in the process. Thyone N was killed nine days 

 after self mutilation. At the injured end there was a 

 very small plug of tissue representing the newly formed 

 esophagus; a thread-like continuation of this tissue, the 

 beginning of a new stomach-intestine, was also seen in 

 the mesentery. The calcareous ring and the ring canal 

 were not clearly denned. Another Thyone was killed at 

 about the same age after evisceration ; India ink was in- 

 jected into the cloaca and into the opening at the ante- 

 rior end in an attempt to demonstrate a cavity in the 

 newly formed thread-like, stomach-intestine. The re- 

 sults were negative and the esophagus was found to be 

 tightly closed. However, the interesting observation was 

 made that the anterior end of each of the longitudinal 

 muscles had split off a very slender branch to form a 

 new retractor muscle (see Fig. 3). These newly formed 

 retractor muscles were not more than one fourth inch in 

 length; their anterior ends were attached in a normal 

 position around the esophagus, but their posterior ends 



