520 C. M. Child. 



or of parts are much less powerful, and consequently the pressure 

 exerted upon the anterior region by such contractions through 

 the intestinal contents or other fluids in the body are greatly 

 reduced. In the other eight pieces the head region functions all 

 the more actively because parts are missing and the stimuli re- 

 ceived from them are absent or received in a nev^ manner. In 

 this piece, hoM^ever, the movements of the head region are very 

 slight. In short, all or nearly all the functional conditions 

 characteristic of the head region are absent or greatly reduced. 

 Here again as in connection with posterior regeneration (Child, 

 '04b) we find a close parallelism between functional activity and 

 power of regeneration. The significance of the facts will become 

 still more evident in the light of further data given below. 



Description of other series would only multiply details without 

 adding anything essential. All specimens cut through the middle 

 or anterior half of the ganglia behave much like normal animals 

 and regenerate rapidly and completely while those in which only 

 a small part of the ganglia remains behave much like specimens 

 without ganglia, never regenerate a head, and apparently lose 

 the small portion of ganglionic tissue by degeneration. The 

 amount of new tissue regenerated is sometimes more and some- 

 times less, but, as will appear below, various conditions may 

 determine such diff'erences. 



In the preceding section (p. 514) the statement was made that 

 the greater the part of the head removed anterior to the ganglia 

 the greater the rapidity of regeneration. This fact is well illus- 

 trated by a comparison of the series described in that section 

 (Series 16) with Series 17 described above. Both of these series 

 were begun on the same day and both were examined at the same 

 intervals so the results are strictly comparable. Figs. 2, 3, 4 and 

 5 represent stages of Series 16 corresponding, respectively, to the 

 stages of the eight pieces of Series 17, shown in Figs. 7, 8, 9 and 

 10. Fourteen days after section the pieces of Series 17 (Fig. 9) 

 have regenerated about twice as much tissue as those of Series 16 

 (Fig. 4). Eighteen days after section regeneration in both is 

 about complete, though the pieces of Series 17 (Fig. 10) have had 

 about twice as much material to replace as those of Series 16 



