In this article we will discuss about the gastrulation and the formation of primary organ rudiments in fishes. In fishes the yolk formed in the oocytes during oogenesis initially does not differ substantially from the yolk in amphibian oocytes and eggs. It consists of yolk platelets lying in the cytoplasm and intermingled with other cytoplasmic components (mitochondria and the like). [...]
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 [...]