2QO LEONARD P. SAYLES. 



these much enlarged cells, that " the neoblasts have a redifferenti- 

 ating effect upon the cells of the ectoderm." A close examination 

 of the facts, however, demonstrates that the cases which he 

 cites in proof may all be explained in another way. 



In the course of regeneration the enlargement of the hypo- 

 dermal cells does not appear to begin suddenly soon after the 

 arrival of neoblasts at the wound. It seems rather to be a 

 continuous process having its inception at the time the worm is 

 cut. A certain time is required for the cells of the hypodermis 

 to enlarge and those on the ventral side do not change any 

 more rapidly than those elsewhere. They do, however, show a 

 greater response than the others with the result that their 

 enlargement continues after the others have slowed down. In 

 sections of twelve-hour regenerates the ectoderm is quite different 

 from that in uninjured individuals and the process of enlarge- 

 ment is clearly under way. At this time neoblasts are rarely 

 found at the wound. Krecker ('10, p. 422) says that "twelve 

 hours after the operation ... in one of these (individuals) 

 there was a neoblast at the w r ound, but none was migrating. 

 In the other individual . . . two were about the wound." If 

 it is true, then, that the enlargement of the ectoderm begins 

 before twelve hours after the cut is made, and it certainly appears 

 to, it is improbable that the neoblasts could have been the cause. 

 A much simpler explanation, which seems to satisfy all of the 

 requirements of the facts at hand, is that whatever is the under- 

 lying cause of the metamorphosis of the neoblasts on the septa 

 is likewise the cause of the enlargement of the cells of the hypo- 

 dermis at the wound. Just what may cause the neoblasts to 

 metamorphose is not discussed by Krecker. 



This view that the transformation of the ectoderm cells is 

 independent of the presence of the neoblasts is entirely in accord 

 with the cases cited by Krecker ('10) in proof of his theory. In 

 one individual (p. 433) "even after three days there was no 

 enlargement of the ectoderm. No neoblasts were about the 

 ectoderm, in fact there was only one neoblast to be seen and 

 this was along the nerve some distance away." He says later 

 (p. 436) that this "exception cited in 'which no change in the 

 character of the ectoderm cells occurred in the absence of the 



