Mouse embryos can be staged according to a variety of criteria, the most general of which are those described by Theiler in "The House Mouse: Atlas of Mouse Development" (Springer-Verlag, New York, 1989)(Online electronic version). Theiler's criteria are too broad to distinguish many of the important phases of early development and must therefore be supplemented by others, for example, cell number, somite number or those characteristics used by Downs and Davies (1993) Development, 118, 1255. Embryos of the same gestational age may differ in their stage of development. Different mouse strains develop at different rates and, in some cases show differences in the relative rates of development of different organs. Strictly, the stages recognised by Downs and Davies apply to outbred mice of the PO strain. The embryos used in this atlas are collected crosses between F1 and F2 hybrid (C57BL X CBA) mice and this is shown in the information i tab on the selector page.
For embryo models shown we study the surface characteristics; for younger embryos we can where possible count somites ; for older embryos we take note of the development of the eye, limb and tail formation and then following OPT scanning we will give an embryo a theiler stage taking all details into account. Although not of the actual reconstructed models we have made surface water movies to assist embryologists in giving a definitive theiler stage.