1 82 INDIVIDUALITY IN ORGANISMS 



highly conclusive. The assumption of self-determined 

 polarity and symmetry in protoplasm is simply super- 

 fluous, and the burden of proof is upon its supporters. 



Of course the metabolic gradients present in one 

 individual may persist in the parts when that individual 

 divides, so that in such cases the axial relations of the 

 new individual are predetermined. This is the case in 

 fission in Planaria (pp. 92-96) and in many other forms. 

 Apparently also the gradient in a reproductive body, 

 e.g., many eggs, is often determined by its relations of 

 attachment, nutrition, etc., to the parent body. 



In pieces of Tubularia, Corymorpha, Planaria, and 

 many other forms, the original polarity gradually dis- 

 appears as the length of the isolated piece decreases 

 until it becomes practically apolar, and new polarities 

 arise in relation to conditions at the cut ends (pp. 97-101) . 

 This fact indicates that polarity is rather a matter of 

 relation of parts than a fundamental property of pro- 

 toplasm, for in fractions of the axis below a certain 

 length it disappears. 



In nature a particular kind of individual shows certain 

 characteristic axial relations; it is radially or bilaterally 

 symmetrical, or a combination in a characteristic way 

 of radial and bilateral arrangements. But the char- 

 acteristic axial relations are not invariable; they appear 

 regularly merely because events follow the same course in 

 successive generations. In plants the axial relations 

 can be altered in many ways and by many external 

 factors. Bilateral symmetry may be transformed into 

 radial or radial into bilateral, the position of branches 

 may be altered from alternate to opposite or to whorled, 

 and so on. The bilateral tentacle groups on the rings 



