User:Corey Bear/Notebook/(17 July 2014) Embryology & Zebrafish

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Intent: The intent of this experiment was to learn the stages of embryonic development and compare embryonic development in different organisms.

Overview: This experiment was separate from the transect procedures conducted previously, but supported the understanding of vertebrate development in the phylum which were annotated in the previous transect logs, Invertebrates. To complete this experiment, four separate vertebrates were observed under a compound microscope and dissecting microscope (the exception was the human) to understand the three stages of embryonic development, fertilization, cleavage, and gastrulation. The four vertebrate observed—which correspond sequentially to Table One & Two—are the starfish, frog, chick, and human.

Observations: The Starfish was not physically observed, but a reference of the embryonic process was presented via a model. The starfish fertilizes the egg in a isolecithal method, but requires an external aquatic setting to facilitate the process. Cleavage occurs approximately an hour to two hours after fertilization in a holoblastic method, which creates a blastula. This blastula eventually separates to create the three germ layers—ectoderm, endoderm, and mesoderm—seen in the starfish anatomy (Bentley, ‘'et al, 2014). All addition information regarding the embryonic development can be found in Table One & Two.

The Frog also followed the external aquatic fertilization seen in the starfish, but through a sexual process called amplexus; where eggs are release by pressure put forth on the female frog by the male forcing the eggs to release into the surrounding water, followed by sperm into the surroundings as well. The cleavage process is teloecitchical, which means the yolk within the egg is in a vegetal hemisphere. During glastrulation, blastopres are formed which create the three germ layers, and later on to tadpoles, which are the larva that develop into frogs (Bentley, ‘'et al, 2014). All addition information regarding the embryonic development can be found in Table One & Two.

The chick fertilizes internally as a terrestrial, which means the process begins on land and within the mother. During fertilization, a germinal disk, which can be found on the cytoplasm of the yolk in the egg, forms, which later becomes the embryo. Albumin surrounds the yolk and provides nutrients to the embryo with in a harder shell porous to gas. The cleavage process is unique in birds, as the yolk has excess amounts. This hinders the division of the cells and creates a blastodisk that later becomes the germanic layers through the transformation of the blastocoel. Gastrulation of the chick occurs differently in the terrestrial chick, than that of the aquatic vertebrates mentioned previously, through a process called primitive streak. This process involves cells moving across the blastodisk that spread out to form the mesoderm. During further development of the egg and embryo, the chicken keeps the eggs warm until it is fully developed and ready to hatch (Bentley, ‘’et al, 2014). All addition information regarding the embryonic development can be found in Table One & Two.

The human fertilization occurs through a sexual process, where a male and female mate. This process involves the transfer of sperm in to the female counterpart, where the sperm travels into the fallopian tubes to penetrate fertile eggs of the female. This process is isolecithal and the cleavage is holoblastic. Unlike the previously mentioned species, the human embryo takes nutrients and disposes of waste through an umbilical cord. The embryo is proctected through thousands of villas, which form in the cell wall of the mother to create a placenta. The placenta enables the umbilical cord to function properly, as it operates from the mother’s circulatory system, thus, the embryos fate is directly related to the health and safety of the mother. This process differs from many other species, as it is extremely costly on the mother, not only during pregnancy, but the years following during early development (Bentley, ‘’et al, 2014). All addition information regarding the embryonic development can be found in Table One & Two.

Table One:

Table Two:


Distribution of Yolk:

Three Layers:




Bentley., Walters-Conte., & Zeller. (2014). Biology 210 Lab Manual. Washington: American University.