Developmental biology is partly concerned on the study of the formation of life which is known as embryology. Developmental biology focuses on how all forms of life begin and how they have developed fully into functioning organisms while the focus of embryology is much narrower. Embryology deals with the study of formation of life and living things. An embryonic study of fish eggs and frogs is fairly discussed in this article.
The embryonic development of a vertebrate egg can be studied under a microscope using an ordinary aquarium fish or a zebra fish. A Brachydanio rerio lays about a hundred eggs in the water as the female dashes rapidly up and down the length of the aquarium tank. Observe the habits of the fish and be prepared with a pipette, to take out some eggs from the finger bowls filled with aquarium water. Keep the water temperature at 80 degrees Farenheit and change it everyday using water of the same temperature.
Move a single egg in a microscope glass slide keeping the well filled with water at correct temperature. Study the egg under a low powered microscope objective and observe the process of repeated embryonic cell division. A new zebra fish is a perfect example to observe under a microscope to see the living cells divide its substance into two, four, eight, sixteen, thirty-two segments knowing that the end product is the development of a new organism. A new cell division occurs once every twenty minutes under optimum circumstances.
A pond inhabited by frogs can supply a student with a source material for their microscopic and embryonic observation. You can found many different sizes of frogs and frogs eggs at the pond. These eggs are best to be collected in a pail of water and are transported to the laboratory where they are cultured for further microscopic observation for embryonic study.
Fill up the bowls using pond water to the middle mark. Spoon a group of eggs into each finger bowl tenderly and change the water each day to keep the culture going. Aged tap water may be used, if the supply of pond water is worn out. To discover the various embryological stages in the development of the frog, examine the egg mass at intervals by positioning it over the microscope glass slide. Few hours after the frogs have spawned, cell division occurs.
Eliminate the protective jelly like coating of the frog to be studied before placing it over a microscope glass slide, to observe it better. Separate an egg from a batch and gently roll it on a piece of blotting paper until the paper absorbed the jelly. Fix the egg with a folmol-nitric solution or in Smiths fixative if the specimen is to be preserved or mounted. To make structures and details more visible, bleach out some of the dark discoloration through an overnight bath in hydrogen peroxide.
Notice the frogs eggs division into an upper and a lower half marked by a dark colored upper hemisphere and a light-colored lower hemisphere. Observe as cleavage begins to form, the way division occurs at the two, four, and eight cell stages. Divide more rapidly in the upper hemisphere with the eventual evolution of a hollow ball of cells, the gastrula stage.
Look for a groove on the surface of the developing egg over the microscope glass slide in the later stages of development. This groove is the neural tube. This will eventually develop into a spinal cord, the characteristic that associates the frog with other vertebrate animals.
Though not without some attendant difficulties, it is a worthwhile project to try raising some eggs to the tadpole period and thence to maturity. The metamorphosis of a frog is one of the natures greatest lessons seen only under a microscope.
