The hypothesis that sub-cellular components of chicken muscle homogenates can induce the differentiation of primitive muscle cells within the chick chorioallantoic membrane (CAM) has been examined. Sterile cell-free homogenates of chicken and mouse skeletal muscle were applied to the CAM utilizing a false air-sac technique. Other experimental groups received, in lieu of muscle homogenate, Cab-O-Sil silica gel, lyophilized albumin, exposure to incubator atmosphere, or Ringer solution. Histological examination five days after treatment revealed the longitudinally oriented elongated mesoderm cells considered primitive muscle by other investigators. However, these cells were noted not only in membranes treated with muscle homogenate but also in all other experimental groups except that receiving only Ringer solution. It is therefore concluded that regardless of the true cellular nature of the longitudinally oriented elongated mesenchymal derivatives described, they do not represent a specific inductive phenomenon but rather a component of the general reaction to injury of an exceptionally labile system. Caution, consequently, is urged in subsequent studies of the chick CAM which utilize present histological techniques. © 1965.