Like fish eggs, chick eggs are telolecithal and undergo meroblastic cleavage. Chick development has traditionally been presented in embryology and developmental biology courses because of the accessibility of embryos at desired stages. As well, it is a good model for understanding vertebrate development in general and mammalian development in particular. Remember, you are not just looking at the embryos; you are studying them to understand how the embryo is formed.
You should study the embryo by examining the material prepared by Dr. Steven Scadding at The University of Guelph at his Web site, Developmental Biology ONLINE. This link will take you to the introduction homepage of the 24-hour chick embryo. It is crucial that you read and understand the explanation given on how to navigate through the 15 photographs of the chick embryo. After you have carefully read this, click on the "GO! To the site" button.
Movie: Ch_24hr.Mov. Next, you should use this movie to obtain an overview of the 24-hour chick embryo and to obtain a sense of the structural continuity of the embryo. This film was compiled from photographing serial cross-sections of the embryo.
Use the same procedure as for the 24-hour stage. A detailed analysis of the 48-hour chick has been prepared by Dr. Scadding. Again, the homepage for the 48-hour chick must be thoroughly understood before proceeding.
Hint: The cranial flexure of the embryo makes the head of the chick point caudally, so that the most anterior section is the midbrain. The dextral torsion refers to the twisting of the embryo whereby the left side of the anterior half rests upon the yolk, and the posterior half remains dorsal-ventral with respect to the yolk.
There are 45 sections to view. You will not have enough time to analyze them in depth and identify every structure. Be sure that you can identify the following:
Movie: Ch_48hr2.Mov. Now examine the movie of the 48-hour chick embryo cross-sections and try to identify the above structures in the various sections.
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Leon Browder & Laurie Iten (Ed.) Dynamic Development
Last revised Wednesday, July 29, 1998