414 E. I. WERBER 



The deformities observed in duplicities are of the same nature 

 as those of other monsters, i.e., they are, usually, due to some 

 defects and, sometimes, 10 to an inhibition in development. 



It is relatively easy to account for the genesis of defects as 

 the result of lesions produced by osmotic pressure. 11 The 

 latter, however, will not account for an inhibition of develop- 

 ment such as may be found in some monsters and, occasionally, 

 in one or both components of a duplicity. As I have pointed 

 out elsewhere (Werber, '15 and 16 b) for this form of deviation 

 from the ontogenetic norm we must assume chemical altera- 

 tion as responsible for the decrease of the germ's inherent capa- 

 city for development and differentiation. This assumption 

 will account for such deformities observed in duplicities as may 

 properly be regarded as due to an inhibition. 12 



Moreover, chemical action may play a much greater part in 

 contributing to the genesis of defects by either directly destroy- 

 ing certain parts of the germ or by lowering their resistance to 

 the action of osmotic pressure. The combined action of these 

 factors (osmotic pressure and chemical alteration) may result in 

 any conceivable monstrosity depending entirely upon its degree 

 and upon the part of the germ which has suffered most from it. 13 



Keeping this in mind we shall be able to understand how not 

 only (variously malformed) duplicities may result from the 



10 Rarely. 



11 This assumption is justified in view of the effects of osmotic pressure direct- 

 ly observed by Loeb (I. c.) in the sea-urchin. It should also be noted thatLoeb's 

 method — decrease of external osmotic pressure by diluting the sea-water — ex- 

 cludes altogether the possibility of chemical action. 



12 In previous papers I ('15 and '16 b) have defined inhibition as a decrease 

 of the germ's originally inherent 'chemomorphic' potentiality. This concep- 

 tion is based on the exceedingly suggestive hypothesis advanced in the last two 

 or three decades by a number of biochemical authors and most recently present- 

 ed in a very succinct and attractive form by Reichert ('14), according to which 

 the development of an organism is a complex series of reactions in a stereochemical 

 system. Reichert's paper came to my attention through the kindness of Prof. 

 H. V. Wilson after the completion of the manuscript for the present paper. 



13 The theory of blastolysis was presented rather exhaustively in a former 

 paper (Werber '16b). Owing, however, to misrepresentations which it suffered 

 at the hands of certain authors the reader will; I hope, find that a repetition of 

 its salient points in this paper is justified. 



