Waters and Bywaters ('42) described a mutation in chickens which, among other things, resulted in limb deficiencies. The so-called "wingless" condition was due to a recessive mutation and was expressed only in homozygous recessives. Characteristically the wings failed to develop. The wing girdle was normal but the wing itself was either absent or represented by an exceedingly small humeral stump. I n some homozygotes the legs also showed anomalies. Along with limb defects Waters and Bywaters showed that there was a failure of lung development and complete agenesis of the metanephros. The down was frequently clubbed and the embryos were small. A study of the early embryonic stages of homozygotes (Zwilling, '49) revealed that the wing buds were relatively normal during the early part of the third day of development but that there was a loss of an ectodermal ridge from the distal edge of the limb bud during the latter part of the third day and during the fourth day. At the end of the 4th day there was no trace of the apical ectodermal ridge in the wing buds of homozygotes. This correlated nicely with the experiments of Saunders ('48) which pointed to the importance of the apical ectodermal ridge for continued distal limb development.