» Amphibian Embryology Tutorial    Glossary and graphical illustration of oogenesis, cleavage, gastrulation and neuraltion, primarily in Ambystoma and Xenopus, from the University of Wisconsin, Madison.    http://worms.zoology.wisc.edu/frogs/mainmenu.html

» Xenbase    Collection of information on early amphibian development, methods including immunohistochemistry, in situ hybridization, molecular markers, based on Xenopus, as part of the WWW Virtual Library.    http://www.xenbase.org/