Of the four common alkaline earth cations, only Ca++ is able to protect Rana pipiens embryos from dissociation of the epidermis into isolated cells by EDTA. Presumably this is because only Ca++ is able to satisfy the divalent cation requirement for cellular adhesion in this tissue. Although early stage embryos are completely dissociable by EDTA, the axial musculature, brain and spinal cord become resistant to dissociation by stage 17. Tetraphenyl boron is also effective in disaggregating amphibian embryo tissues. Copyright © 1968 Wiley‐Liss, Inc., A Wiley Company