Duplicity in Birds

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Abstract
Of 7 specimens of posterior duplicity, 2 had 4 wings and 4 legs; the remainder the legs only. Considerable variation occurred in leg attachment, and in all the spinal columns were double posterior to the cervical region. Internally, the digestive tracts were double behind the gizzard, with either 3 or 4 ceca present. The kidneys were duplicated in specimens with 4 wings and 4 legs, but in 1 case of 2 wings and 4 legs the anlage of the kidneys had divided and there were but 2 kidneys, widely separated. Evidently all cases resulted from posterior fission, as it would be most difficult to conceive of perfect fusion of the heads from independent primitive streaks.

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