Abstract
The posterior third of the primitive streak was implanted into the 2 ½-day chick embryo. Both growth and differentiation of the untreated implants were similar to those of the serum albumin series. Treatment with liver RNA, however, resulted in a significant increase in the rate of growth and differentiation. When liver RNA was incubated with RNase, the products furthered the growth and feather bud formation, but reduced the differentiation of the endodermal derivatives, especially gut.