146 INDIVIDUALITY IN ORGANISMS 



this or some other factor in the environmental con- 

 ditions is the essential one. The important point is 

 that a new metabolic gradient, major axis, or polarity 

 is in these cases determined by external conditions, 

 and that morphogenesis occurs with reference to this 

 gradient. 



In the case of a sea-anemone, Harenactis (Fig. 79), 

 obliteration of the original gradient is accomplished in a 

 somewhat different way.^ The bodies of these animals 

 are tubular, with partial longitudinal partitions, the 

 mesenteries. When the rather bulky mesenteries are 

 not removed, pieces cut from the body close by gradual 

 contraction at each end, the wounds heal, and a new 

 disk and tentacles develop at the apical, and a new 

 ''foot" at the basal end. If, however, rather short 

 pieces are taken (a, h, Fig. 79) and the mesenteries are 

 largely cut away from the interior of the body, the 

 pieces close up and heal as indicated in the longitudinal 

 section (Fig. 80), because there is no mass of internal 

 tissue to prevent the two ends meeting when the piece 

 contracts. In such pieces the apical cut surface of the 

 body wall unites with the basal about the whole circum- 

 ference, and the result is a ring or doughnut-shaped 

 structure which makes an attempt to orient its body as it 

 does in nature by revolving about a circular axis like a 

 vortex ring until the region of union of the two ends 

 lies on its upper or outer surface. 



At this region of union more or less new tissue arises, 

 particularly if the cut surfaces are irregular and do not 



' Child, "Factors of Form Regulation in Harenactis attenuata, I, II, 

 III," Jour, of Expcr. ZooL, VI, VII, 1909; "Further Experiments on 

 Adventitious Reproduction and Polarity in Harenactis," Biol. Bull., XX, 

 1910. 



