114 Cc. H. DANFORTH 
proper nutritional conditions to continue its development to the 
end. If these suppositions are correct it is quite conceivable 
that the whole complex is due to a slight irregularity (delay or 
acceleration) in the beginning functioning of some one or other 
of the endocrine glands. The character of the gland would of 
course be determined by other factors which would have an 
ultimate basis in the nature of the germ plasm itself. An ex- 
planation of this sort, both for these characters and for poly- 
dactyly would much more readily account for the aberrant 
nature of the ratios obtained in breeding experiments. 
SUMMARY 
The observation reported in this paper establish the fact 
that, at least in certain strains of poultry (and probably in 
pigeons) there is a close correlation between brachydactyly 
involving the size and number of bones in the feet, and the 
presence of feathers on the tarsi. The embryology of both 
conditions has been studied, the evidence from this source 
indicating that while the size and number of skeletal elements 
are determined by the length of the embryonic toe, there is no 
causal relation between toe length and feathering. The data 
cited seem to indicate, on the contrary, that brachydactyly, 
feathering of the tarsi, and probably syndactyly are all de- 
pendent on one and the same factor. No attempt is made to 
postulate the nature of this factor but it is suggested that a 
study of the early functioning of the endocrine glands in normal 
and abnormal embryos might throw some light on the question. 
No. correlation could be detected between either of these 
characters and polydactyly or comb form. 
