Abstract
Previous experiments with TEM (triethanomelamine) on chick and mouse embryos (Jurand, 1958, 1959) have shown that some embryonic regions are more sensitive than others to its cytotoxic activity. TEM appeared to be specifically active against mesodermal structures, particularly against the somitic mesoderm, being relatively less active against other tissues. In amphibian embryos, however, the neural tube cells were the most sensitive (Waddington, 1958).