Handout for Laboratory 12, Vertebrate Zoology 03051: Vertebrate Development
Lab manual (Hickman et al., 9th ed.): Exercise 4B, pp. 51-52, 53-55; Exercise 4C, pp. 59-61
Text (Hickman et al., 7th ed.): Ch. 11, pp. 248-250; Ch. 14, pp. 318-337
WORD BANK: terms/structures to find and know from this lab.
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Materials include: models #1-10 of sea star development (grey stands); models #1-20 of frog development (wooden stands); whole mount slides of chick development. Times represent hours after fertilization: 16 hours, 24 hours, 33 hours, 48 hours, 72 hours (five slides in all). Chick embryo composite model: (through approximately 33 hour stage).
This two-hour lab is not intended to make you an expert in vertebrate embryology, but rather is intended to give you an overview of the major processes involved. By the end of the lab, you should be able to recognize the general"flow" of events, and the appearance and location of major organs and organ systems as they appear in different vertebrate embryos. Your lab manual contains nice diagram of the events in sea star and frog development in Exercise 4. Included with this handout are some labeled diagrams of the chick embryo, although your text (p. 322) highlights the initial events of chick development.
Sea star models. These represent the"typical" pattern of radial cleavage. Note how the zygote through radial divisions progresses from a morula (solid ball of cells) to a blastula (hollow ball) made of many blastomeres (the individual cells) and with a blastocoel (internal hollowness, but note that the coelom or body cavity will be derived from the mesoderm germ layer!). The"folding in" of gastrulation at the blastopore helps to create ectoderm and endoderm germ layers, as well as the archenteron (the future gut tube). Sea stars and chordates are deuterostomes--the blastopore represents the future anus.
Frog models. These parallel the series on p. 60 of the lab manual for the most part. Note that frog eggs contain more yolk than sea star eggs, so that 1) a dorsal animal hemisphere is present to form the embryo and 2) much of the ventral part of the organism is involved with yolk. Note how many of the early frog stages are otherwise similar to that seen in the sea star . By models #12 and 13, the notochord and neural folds should be obvious. The neural folds form a dorsal hollow nerve cord (the frog is a chordate, right?), which continues to elaborate into the brain at the anterior end. The ventral heart and the blocks of skeletal muscle or somites are also visible in the later frog models. Internal mesoderm that will contribute to urogenital and gut organs is also visible.
Chick slides. As you are familiar with from the grocery store, chicken eggs contain a lot of yolk! As a result, the embryo looks a bit more flattened and distorted than even seen in the frog. At 16 hours, the major feature is the primitive streak, or a anterior-posterior fold and groove equivalent to the blastopore. At 24 hours, the head end is prominent, with neural folds ready to form the brain and the spinal cord. Somites, or blocks of skeletal muscle, and the stiffening notochord appear here as well. The 33 hour chick slide has large optic vesicles and more brain swelling--can you start to identify forebrain from the other parts of the brain? The notochord is a thin, dark-staining structure ventral to the nerve cord. The heart is now visible, as are more somites. The 48 hour chick shows an increasing definition of these major structures, in addition to the forming ear and eye, and the 72 hour chick begins to show limb buds. A chick hatches in three weeks, so that you see that the organ systems set up early in vertebrate development!
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This web page last updated on April 24, 2000
