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It is Easy to Study the Development of the Chick!

L. R. R.

It is unfortunate that many classical aspects of Zoology are rarely studied from the living animal. Text-books with their intimate descriptions have isolated students from actual contact with the processes which the texts describe. Reference to the text seems so much easier than the study of the animal itself, but too frequently the study only of the text leaves the student with a confused understanding and no real appreciation of the subject matter.

Aristotle obviously studied the development of the chick from incubated eggs. Two thousand or so years ago, Aristotle had a more vivid picture of the embryology of the chick than does the average student of this day who knows the subject only as words and pictures in a book. Aristotle must have borrowed the eggs from an incubating hen. He lived probably closer to nature than many of us are living in this day.

Nevertheless it is now a simple matter to obtain fertile eggs from a poultry man. We can place these eggs in a shoe box with straw, warm them gently with a 15-watt electric bulb so that they are kept at a temperature of about 38°C. and then the eggs will develop. If we obtain a dozen fertile eggs, four can be placed in the box one day; four on the next; and four on the third day. The eggs should be marked so that each can be recognised as to the length of its incubation.

On the fourth day, remove the eggs which have been incubated for twenty-four hours. Make a solution of one teaspoon of common salt in one quart of water. Warm this to 38°C. Tap and break the upper surface of the egg to make a hole about one inch in diameter. Tease away the fragments of the shell. With scissors cut away the membrane and gently lower the egg into the warm salt solution so that the egg is covered.

New use a lens. You will see the developing disc of the embryo with a streak on the surface which will become much of the nervous system.

Do this with an egg which has been incubating for forty-eight hours. This will show the forming vesicles of the brain, the spinal cord with muscle buds obvious on either side all prominent on the disc. It may show the rudiment of the eyes, the head beginning to lift from the surface, blood islands and many other details in a reality never to be known only from the text.

The egg which has been incubating for seventy-two hours will show a large head with prominent brain vesicles, many muscle buds, the early forms of the embryonic membranes, a beating heart and flowing blood.

If you would proceed further then cover the egg with the salt solution, gently cut around the edge of the disc to float the disc free from the yolk and float it carefully on to a submerged slide. Raise the slide from the solution. Flood the disc with salt solution. Dry the lower surface and put on a cover slip.

This preparation can be studied with the lens or microscope, drawn in all its detail, and the development of the chick becomes a study of life and no longer a matter of simple memory. This is the time when reference to a text has real value.

There is only one caution to keep in mind. See that the lamp for incubating the eggs is secured so that it cannot overheat and kill the eggs nor be a cause of fire. This is a hazard which was no worry to Aristotle.

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