EXPERIMENTS ON ASYMMETRICAL FORMS AS 

 AFFORDING A CLUE TO THE PROBLEM OF 

 BILATERALlTYi 



HANS PRZIBRAM 



Biologische Versiichsanstalt, Vienna 



ELEVEN FIGURES 

 ONE PLATE 



In bilaterally symmetrical animals we may often find mon- 

 strosities consisting in the appearance of a pair of supernumerary 

 appendages, of which one shows the symmetry proper to its side, 

 while the other, being the mirror image of the former and also 

 of the normal appendage, shows the symmetry of the opposite 

 side. Two photographs, the first of a bull with a supernumerary 

 pair of legs arising from its right shoulder (fig. 1) and the second 

 of a trifid dactylopodite in Cancer pagurus (fig. 2) will serve to 

 illustrate the statement. Is the appearance of appendages with 

 an inverted symmetry really due to the presence there of latent 

 determinants of the opposite bodj^-side, or is it merely due 

 to development of an anlage of its own body-side, the mirror 

 appendage standing in no causal relation whatever to the opposite 

 side? 



A perfectly symmetrical form affords no clue towards the solu- 

 tion of the question, because on such objects we have no means 

 of distinguishing a structure in the proper position but developed 

 in an inverted fashion, from a structure of the opposite side. In 

 .animals, however, where unequally developed appendages are 



^ Translated /rom the German paper read to the Eighth International Con- 

 gress of Zoology at Graz, August, 1910. 



255 



