In this article we will discuss about the development of general body form of vertebrates. While the various organs are being formed, the shape of the embryo as a whole undergoes far-reaching changes. During the period of organogenesis, in the case of the vertebrate embryo, the main changes are: i. Elongation of the body. ii. Formation of the tail. iii. [...]
In this article we will discuss about the gastrulation and formation of primary organs rudiments in birds. The earlier stages of the discoidal cleavage in the eggs of reptiles and birds resemble essentially the cleavage in meroblastic eggs of the fishes. The blastoderm is several cell layers thick, and lies over a "sub-germinal cavity." At a later stage of development [...]
The relation between the archenteron and the definitive alimentary canal is very different in vertebrates with complete cleavage from that in vertebrates with incomplete (meroblastic) cleavage. The Relation in Lower Vertebrates: The archenteron in Amphioxus is originally lined with presumptive endoderm, presumptive mesoderm, and presumptive notochordal cells. When the notochord and the mesoderm are segregated from the endoderm, the latter [...]