Basic Stages in an Animal Development
Animal development is the process that leads to the formation of a new animal or organism from cells that derived from one or more parent individuals. Animal or organism arises through a process that begins with the fertilized egg and ends with a new individual. The fertilized egg will undergo cell divisions to increase the number of cells and simultaneously the cells produced will differentiated into organs and organs systems of the fully formed organism. Animal will go through six basic stages of development. They are fertilization of egg (ovum) and sperm, cleavage, gastrulation, neurulation, organogenesis and metamorphosis (refer to Figure 1 in Appendix 1). The successful development at each stage depends on the successful complexion of the stage before.
The first stage in animal development is fertilization. Fertilization is the process whereby the two sex cells (gametes) fuse together to create a new individual with genetic potential hat derived from both parents. Process of fertilization can occur in two ways; internal fertilization, process
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Gastrulation is an early phase in the embryonic development of animals and results in the formation of three embryonic tissue layers. The first embryonic tissue layer is ectoderm which is the outside layer will ultimately form the outer covering of the adult body and the nervous system. The second embryonic tissue layer is mesoderm which is the middle layer will form muscle, the skeletal system and the circulatory system. Lastly, the endoderm which is the internal layer will form the lining of the gut and other internal organs such as liver and lung. In addition, Professor Lewis Wolpert who is the developmental biologist remarks that "it is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life” (Wolpert, 1986). It means that gastrulation is a very important event in the