140 INDIVIDUALITY IN ORGANISMS 



The metabolic gradient associated with the new 

 head shows a corresponding decrease and increase in 

 length in such pieces. The influence of the new head- 

 region extends to a greater or less distance according as 

 its metabolic rate is high or low, and the position of the 

 various organs is altered correspondingly, or, as in the 

 extreme case of Fig. 69, no new organs are formed except 

 the head. 



When the metabolic rate is high, as in Figs. 66 and 70, 

 dominance extends nearly or quite to the basal end of 

 the piece, though short zooids may be present as more 

 or less distinct gradients (see pp. 92-94) at the basal 

 end. Before section most of this region of the body 

 consisted of one or more zooids, but the development of a 

 head nearer to these zooids than the original head has 

 brought about the obliteration of the gradients which 

 represented them, except perhaps in the extreme basal 

 region, and after reconstitution a single gradient extends 

 over at least most of the length of the piece. When the 

 metabolic rate is lower, as in Figs. 67 and 68, a short 

 individual develops from the apical region of the piece, 

 but most of the broader portion is not physiologically a 

 part of this individual. This is very evident in the 

 behavior of these forms, for, when creeping about, they 

 are unable to control and co-ordinate this region to any 

 great extent ; and simply drag it about like a dead mass. 

 As long as they remain in the narcotic they are not active 

 enough to undergo fission, but if they are returned to 

 water, fission may occur after a few days, although the 

 range of dominance gradually extends, and more and 

 more of the length of the piece comes under the control of 

 the head. 



