No. 613] INHERITANCE IN FAX TAIL PIGEON 25 



feathers, so far as this intimate union in the middle line of 

 the bud permitted. There are no indications that the 

 split feather is due to the union of two separate rudiments 

 that have been pressed together so closely as to interfere 

 with the full development of each when they came in 

 contact. 



The Location of the Sp 

 The location of the split feathers (and modified types) is 

 given in the next table. 



Feather "split" . . . 9 near middle, 1 one quarter from side 



End only split 2 near middle, 1 one third from side 



Double vein at tip. . 2 near middle 



Very unequal parts . 7 near middle, { ? tw ,° tbird * [ T °™ s!de ' 

 1 1 outermost feather. 



In the great majority of cases the doubling occurs near 

 the middle of the tail. The meaning of this is not at all 

 apparent. We know so little about the cause of duplica- 

 tion in general and about the embryological mechanism 

 that is involved in laying down the feathers in the tail, 

 that it is useless to speculate about the result. The evi- 

 dence from experimental embryology shows unmistakably 

 that doubling may result from a mechanical interference 

 with the relation of the blastomeres after they have as- 

 sumed a definite position in regard to each other, but there 

 are also many other cases known where, in normal devel- 

 opment, a part is repeated several or many times. In 

 these cases we can as yet only surmise that the rudiments 

 of the structure— simple cells or groups of cells— become 

 mechanically drawn apart by the more rapid growth of 

 surrounding parts and separated so that each gives rise 

 to a separate organ. Split feathers, from this point of 

 view, would be looked upon as an incomplete separation 

 of certain of the rudiments. However this may be, one 

 can imagine other ways by which a specialized group of 

 cells could become broken up into islands. 



