Cell death during normal gastrulation in the newt, Cynops pyrrhogaster.

Cells falling off from ectoderm were observed in normally developing gastrulae of the newt, Cynops pyrrhogaster, in light microscopic examination. These cells eventually died. The number of such necrotic cells per embryo varied from a few dozen to a few thousand. In embryos with many necrotic cells, the ectoderm was thin, the yolk plug large, and establishment of the neural plate was delayed compared with embryos with fewer necrotic cells. A neural tube of normal size was formed at the tail bud stage irrespective of the number of necrotic cells. A new hypothesis to explain these observations is presented.