AUTHOR’S ABSTRACT OF THIS PAPER ISSUED 
BY THE BIBLIOGRAPHIC SERVICE, FEBRUARY 24 
THE DEVELOPMENTAL RELATIONS OF BRACHY- 
DACTYLY IN THE DOMESTIC FOWL 
C. H. DANFORTH 
Department of Anatomy, Washington University School of Medicine 
FIVE [FIGURES 
The factors which exercise determining influences in the 
ontogeny of animals have proved difficult of recognition and 
evaluation. To what extent any given structure is the direct 
expression of some more or less specific ‘determiner’ in the 
germ cell and to what extent it represents the product. of 
reactions to the influence of other parts of the developing 
organism cannot often be estimated in any reliable manner. 
Nevertheless, some knowledge of the relative weight of the 
two kinds of factors involved is essential to a satisfactory con- 
ception of the processes .of embryology and morphology. The 
observations recorded in the present paper are reported because 
they seem to throw some light on this problem with reference 
to a rather special case; namely, the correlation between skeletal 
peculiarities of the fourth toe and the presence of feathers on 
the tarsi in the common fowl. 
The data to be presented were collected as the result of the 
following observations: In July, 1915, an egg incubated in the 
laboratory hatched out a chick (no. 12) which showed an almost 
complete absence of the fourth toe on each foot. This particular 
chick was helped from the shell and the condition of its toes 
noted at that time, so there is no possibility of the malformation 
having been due to injury received after hatching. Subsequent 
dissection showed that the three terminal phalanges and the nail 
were lacking on both sides (fig. 1, B). During growth the 
lateral rudimentary toes turned under the balls of the feet 
causing the bird some inconvenience, especially in perching. 
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