A correct interpretation of gastrulation is impossible without a knowledge of the position which the presumptive germinal layers occupy in the blastula. This position may be ascertained in various ways. A chart, showing the fate of each part of an early embryo, in particular, a blastula, is called a fate map. In tracing the fate of various parts of the [...]
The changing appearance of the embryos, especially during organogenesis, invites the distinguishing of certain stages which can be referred to when it is desired to indicate how far an embryo has progressed in its development. Tables of "normal stages" have been worked out for a number of species of animals, especially those that are most often used for research. In [...]
In this article we will discuss about the selective affinities of cells as a determining factor in cellular rearrangements of an embryo. We may ask what is the nature of the forces which control the rearrangement of cells resulting from morphogenetic movements in gastrulation and also in other morphogenetic processes; we may ask whether the new positions of the cells [...]