. Embryology. Embryology; Embryology; genealogy. THE EFFECT OF LIGHT ON BREEDING HABITS 19 ber 21 in the northern hemisphere) until the time of their normal breeding season to increasing amounts of light each day. The days get longer during this period of the year. The increase in the amount of light over the amount of darkness each day is the primary factor, then, in controlling the time of ovulation. If in the fall, when the change is in the other direction— that is, when there is more darkness each day and less light—we artificially increase the illumination and thus imitate the spring cond
. Embryology. Embryology; Embryology; genealogy. THE EFFECT OF LIGHT ON BREEDING HABITS 19 ber 21 in the northern hemisphere) until the time of their normal breeding season to increasing amounts of light each day. The days get longer during this period of the year. The increase in the amount of light over the amount of darkness each day is the primary factor, then, in controlling the time of ovulation. If in the fall, when the change is in the other direction— that is, when there is more darkness each day and less light—we artificially increase the illumination and thus imitate the spring conditions, breeding will take place in the fall. Let us now continue the analysis of the effect of light and examine the results of some experiments on birds, which also react to light. These experiments show that the light has no direct effect on the gonads but acts by way of the pituitary gland. In the first place, if the pituitary gland is RATIO OF LIGHT HORMONES IN BLOOD STREAM. Fig. 8. Steps in the stimulation of ovulation. The initial stimulus is a vary- ing ratio of light to darkness. The light entering the eye falls on the retina and stimulates nerve impulses, which reach the brain by way of the optic nerve. In the brain the impulses stimulate the pituitary gland to release hormones into the blood stream. The hormones then travel through the heart and circulation to the ovary. In the ovary they produce changes leading to a breaking of the wall of the follicle, and the egg is released into the body cavity or into the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Barth, Lester G. (Lester George), 1905-1979. New York, Dryden Press
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