V 



EXPEEIMENTS ON ASYMMETRICAL FORMS 263 



instance supernumerary toes of chickens, as was found by 

 Barfurth, Bateson and others. In their experiments, too, the 

 hyperdactyly appeared sometimes on the right, sometimes on 

 on the left and sometimes on both sides quite independent of the 

 parental condition. Although generally dominant, hyperdactyly 

 may in some individuals become recessive, reappearing again in 

 the next generation as a typical dominant. This fact is explic- 

 able according to my view, namely, that in each egg the "plus 

 toe Anlage" is redistributed, so that it goes either to the right or to 

 the left, or to both sides of the body, or even to parts of the body 

 not capable of producing toes, in w^hich case the Anlage does not 

 become manifest. I may also add that Kammerer produced 

 symmetrically spotted Salamandra maculosa from irregularly 

 spotted parents, in which the yellow blotches had been enlarged 

 by keeping them on yellow soil. We find here that the induced 

 'plus' of yellow in the parents, is redistributed in their young 

 according to the bilaterality of the body. 



IV 



From all these facts derived from the stud}^ of regeneration, 

 ^embryology and heredity, may we not draw the conclusion that 

 there are no distinct determinants for right and left body-sides; 

 but that the bilaterality depends entirely upon the distribution 

 of anlagen in opposite directions with reference to the dorso- 

 ventral and antero-posterior axes? True, it seems difficult to 

 reconcile the conclusion with those asymmetries, which are con- 

 fined not merely to minor parts, but are manifested in the struc- 

 tural plan of the entire organism, as for instance the asymmetrical 

 position of the heart in vertebrates or the dextrosity of snail 

 shells. But such asymmetries are transmitted unchanged from/ 

 one generation to the other, and the question therefore arises/ 

 if for these cases we must not postulate specialized anlagen for 

 right and left body halves, each incapable to replace the other? 

 I believe we must not, because, even though rarely, we do nevQt- 

 theless find a reversal of the fundamental asymmetry, as the 

 ''situs inversus viscerum" in vertebrates or sinistrosity in 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 10, NO. 3 / 



APRIL, 1911 



