100 INDIVIDUALITY IN ORGANISMS 



These double apical regions and heads have been 

 observed by many investigators in various animals and 

 have commonly been called axial heteromorphoses, 

 because the apical structure at the basal end of the piece 

 was regarded as something which was out of place and 

 abnormal. This, however, is not actually the case, for 

 the development of these double or biaxial structures is, 

 as I have shown, subject to exactly the same laws as the 

 development of the usual single individual, only in these 

 pieces the conditions are such that the original gradient 

 is almost absent, and the increased activity at the basal 

 end may establish a new gradient in the reverse direction, 

 although some indication of the original gradient may 

 remain in the smaller size or less complete development 

 of the part at the basal end. In these short pieces, in 

 fact, the original polarity is almost obliterated and the 

 establishment of a new reversed polarity in relation 

 to the basal cut end is possible. At each end the 

 relation between the metabolic gradient and the devel- 

 opment of an apical structure is exactly the same as 

 in any other case of development. The apical region 

 arises at the apical end of the gradient and the devel- 

 opment of other parts follows as far as the gradient 

 extends from each end, or in the case of single struc- 

 tures as far as the length of the piece permits. By 

 means of the susceptibility method I have been able 

 to demonstrate these relations between the metabolic 

 gradients and the single or double development of such 

 pieces. 



The development of biaxial or multiple apical struc- 

 tures from pieces has been observed in various other 

 animals, and, while their relations to the metabolic 



