Multiple neural inductions in area opaca by grafts of the Hensen's node do not retard host chick embryo development.

Four hundred and forty four full primitive streak stage chick embryos were cultured in vitro and 261 were transplanted with 1, 3 or 5 Hensen's nodes in the area opaca. Irrespective of the number of grafts, neural induction was observed in 90% cases. The development of control and grafted embryos and the size of blastoderm area were monitored at the time of grafting and after 20 hr. We find that the induced neural tissue and differentiated tissue of graft-origin neither fuse with the host embryonic axis, nor retard its development.

Cell population growth in chick blastoderms cultured in vitro.

Primitive streak stage chick blastoderms were cultured in vitro up to 30 hr by New's technique. Chick blastoderms reaching stages 4 to 12 in vitro cultures and in ovo were harvested and homogenized to release cell nuclei. Fluorescent ethidium bromide-stained nuclei in homogenates were counted in Neubauer's chamber and the size of total blastoderm cell population was determined. Linear regression analysis revealed that both in ovo and in vitro chick blastoderm cell population grows in a biphasic manner with comparable cell population doubling times and the morphogenesis is not affected in vitro during the culture period.