Snell, using a technique described by Fekete et al. The sections were prepared by Olive Bartholomew, Elizabeth Fekete, and G.D. More embryos of a single stage have been sectioned. The material used in this study is the same as that used in 1941 and consists of sections of embryos spaced at 6-hour intervals from 4 to 9 days.

Grüneberg (ġ963) surveyed the field of developmental pathology of the skeleton, including many inherited malformations of the mouse.

Grüneberg (ġ943) has provided a very useful description of mouse development from 9 1/3 to 18 1/3 days, and Otis and Brent (ġ954) have compared human and mouse developmental stages. For other descriptions the reader is referred to Boyd and Hamilton (ġ945) described early development of the golden hamster. Only a few have attempted a comprehensive study. Since 1941 there have been many investigations devoted to certain aspects of mouse embryology, but Will make it clear when we discuss information obtained from the rat. In general there is much similarity in the development of Muridae, but we

Published since then, and some of this was based on investigations on the embryology of the rat. Most of the new information was obtained from a search of the literature This description of the early embryology of the mouse is a revision of Snell's (ġ941) description in the first edition of the Biology of the Laboratory Mouse.

Early development stages blastopore