218 CHARLES R. STOCKARD 



7. THE DOUBLE INDIVIDUAL WITH UNEQUAL COMPONENTS AND 



AN UNDERSTANDING OF THE CAUSE OF ALL 



MONSTROUS DEVELOPMENT 



The most valuable material that falls into the possession of 

 the investigator attempting to analyze the causes of abnormal 

 development is furnished by the united twins and anterior dup- 

 licities where one component is fully developed and perfectly 

 normal in structure, while the other component presents in a 

 series of such forms various degrees or combinations of mal- 

 formation and deformities. There are practically numberless 

 attempts, from the time of Aiistotle until now, at theoretical 

 explanations for the cause of monstrous development, but none 

 of these, as far as I know, have recognized as crucial the con- 

 dition presented by the combination of a larger normal twin 

 developing in actual union with variously deformed lesser indi- 

 viduals. Certainly, all theories that conflict with this condition 

 of fact may be discarded as being inadequate in general. And, 

 as mentioned before, the explanation of abnormal development 

 probably lies in the differences between the factors operating 

 on the development of the two connected individuals. 



In the first place, one could scarcely state in the presence 

 of these specimens that the abnormalities of the lesser compo- 

 nent are of germinal origin. Yet similar deformities in single 

 individuals have been interpreted in Wilder's ('09) theory of 

 'Cosmobia' as always being of such origin. The larger and 

 smaller members of the double complex have both arisen from 

 a single fertilized egg. There is no trace of either direct or col- 

 lateral evidence to indicate that the hereditary factors are not 

 equally distributed in the cells of both components. The germinal 

 origin of one component could in no way be different from that 

 of the other, since the entire specimen was a single individual up 

 to about the stage of gastrulation. Further, when the two 

 components are of equal size their identical genetic composition 

 and character is evident. Obviously, then, defects similar to 

 those enumerated as occurring in the smaller component are 

 not in general of germinal origin. 



