BRACHYDACTYLY IN THE FOWL fale 
If this is the case the question presents itself as to whether the 
relation is causal, one condition producing the other or whether 
the two conditions are both dependent on some one determining 
factor. It was at first thought probable that the abnormal 
development of feathers or down on the feet overtaxes the 
nutritional supply of the limb with the result that the fourth 
toe becomes somewhat stunted in its development. The em- 
bryology of the condition, however, does not support this view. 
On the contrary, in light of the sequence in which the character- 
istics make their appearance in ontogeny, brachydactyly would 
seem to be the cause of feathered tarsi, an interpretation which, 
a priori, does not seem plausible. 
Since, on the whole, the evidence does not favor the idea 
that either condition is really the cuase of the other the only 
alternative that would seem to be left is that they are both 
caused by the same factor. The close association of the two 
characteristics and the fact that they tend to fluctuate together, 
points strongly toward this conclusion. What the factor may 
be or precisely how it acts cannot at present be answered. Nor 
can the number of characteristics which it affects be stated 
since it is quite possible that some of them have been overlooked 
in the present study. 
If the connection between brachydactyly and booting had 
been a little less obvious the former might have been described 
as an independent unit character and a separate determiner in 
the germ plasm postulated for it, as has already been done for 
booting by the several authors who have studied that character. 
In general the relations here described would seem to be such 
as tend to support the contention of Morgan (loc. cit.) that the 
determiners in the germ plasm are not strictly specific, but tend 
to influence the character of the organism as a whole. 
In the particular case under consideration it is quite possible 
that the determining factor may actually be effective for only 
a short time, possibly a few days. After two cartilages have 
once fused it is doubtful if the removal of the exciting cause 
would in itself induce them to separate. It is also possible that 
a feather germ once formed would need no further stimulus than 
