TWO FIQURESPolydactylism is a well-known and ancient mutation of fowl. In its most typical manifestation it accounts for the presence of five instead of four toes on each foot and as such is a standard trait of several breeds of chickens.Polydactylism of fowl is produced by duplication of the anlage material for the first digit. The type and degree of this duplication are very variable and the many resulting forms of expression haVe been the subject of repeated morphological description. All observations on the genetic behavior of polydactylism in chickens have been based on the structure of the toes.It was shown, however, by Barfurth ( '10, ' 11, '14) that the wings are also involved in the expression of polydactylism. He found in embryos of polydactylous breeds (Houdan, Orpington, Silky) that on the eighth day of development a small bud-like structure appeared on the radial margiii of the hand. This protrusion increased in size during the ninth and tenth day, at the same time acquiring a somewhat more finger-like independence. The formation of pre-cartilage and of small amounts of cartilage were observed, but this did in no case progress to the appearance of phalanges. On the tenth or eleventh day the finger-bud became constricted at its base and this constriction continued until finally the primordium was lost. A similar account of the formation and subsequent loss of such a transitory finger primordium was given by Schmalhausen ('34) for embryos of Faverolle fowl.We had occasion to make extensive observations on wings of embryos and chicks from polydactylous stock of Houdan-crossbred and Dorking origin. The following results seemed worthy of record.
APPEARANCE AND PERSISTENCE OF SUPERNUMERARY DIGITSIt was possible in our material to distinguish as early as the beginning of the eighth day of development between the presence and ab-225
ONE FIGUREPolydactyly is a well-known hereditary trait of fowl. It is characteristic for three breeds (Houdan, Dorking, Silkie) , and generally leads to the presence of five toes on each foot, instead of the normal four. The polydactylous condition arises by a splitting of the first toe. Asymmetrical occurrence of polydactyly is rarely found in polydactylous breeds, but is fairly common among the progenies of outcrosses betweeii polydactylous and non-polydactylous chickens.As part of a more comprehensive investigation of polydactyly in fowl, it was decided to study the relations, if any, which unilateral polydactyly has to the frequency of the different types of motor neurons in the two anterior horns of the lumbo-sacral spinal cord.
MATERIAL AND METHODSWe used for our observations twelve adult chickens (eight females, four males) of Houdan-crossbred origin. These twelve birds fell into the following groups: four had five toes on the left foot and four on the right (to be designated as " 5 4 " ) ; three had four toes on the left and five on the right foot (4-5) ; two were polydactylous on both feet (5-5) ; three were non-polydactylous (4-4).
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