352 H. H. NEWMAN 



In conclusion, then, we may give as our general causal theory 

 of twinning (including the doubling of all normally single structures) 

 that the first step involves retarded development, followed by loss 

 of organization or dedifferentiation; that recovery or acclimation 

 results in the formation of new apical points, and the new apical 

 points form the head ends of new individuals. 



LITERATURE CITED 



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Newman, H. H. 1913 The natural history of the nine-banded armadillo of 

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1917 The biology of twins. Univ. of Chicago Press. 

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 1921 b On the occurrence of paired madreporic pores and pore canals 

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