STUDIES ON THE PHYSIOLOGY OF REPRODUCTION IN THE DOMESTIC FOWL

Abstract

1. During the last six years more than three thousand different domestic fowls, which have been kept at least one year at the Maine Agricultural Experiment Station, have laid but three triple-yolked eggs. 2. Each of these eggs was laid by a different individual and in each case the triple-yolked egg was one of the first eggs produced by a young pullet. 3. Young pullets also show a decided tendency to produce double-yolked eggs when they first begin to lay. About 20 per cent. of the pullets which lay before they are seven months old lay among their first eggs one or more with two yolks. 4. Nearly 80 per cent. of the individuals of the flock never lay a double-yolked egg. 5. Mature birds also sometimes produce double-yolked eggs; but most such birds have also produced one or more when they were young pullets. 6. There has been no bird in the experiment station flock with which the laying of double-yolked eggs was "habitual" although there are some which have produced several such eggs. 7. The production of an egg with two or three yolks represents the extreme of rapid egg production, other forms of which are found in the production of two eggs united by a membranous tube; two eggs at the same time; two eggs at different times on the same day and a daily egg production where the eggs are laid earlier on each successive day. 8. The two yolks of a double-yolked egg may have all the egg envelopes in common, indicating that they have passed the entire length of the duct together; or each may possess one or more separate envelopes. There are also all the possible intermediate forms indicating that the two yolks in a common shell may unite at any point between the mouth of the funnel and the isthmus. When two eggs come together after the first has entirely passed the anterior end of the isthmus the result is the production of two eggs at the same time. 9. Various disturbances of the normal processes of egg production may bring two yolks together in the oviduct. Double-yolked eggs evidently do not always represent simultaneous ovulations. The assumption of simultaneity or abnormally close succession of ovulations is necessary to account for the production of a succession of double-yolked eggs or of a double-yolked egg immediately following a long series of normal daily eggs. 10. The double-yolked eggs contain more albumen and have a heavier shell than single-yolked eggs, and in triple-yolked eggs these parts are heavier than in double-yolked eggs. Yet these parts do not increase in direct proportion to the increase in the weight of yolk. That is, the percentage of albumen and shell is less in double- than in single-yolked eggs and is still smaller in triple-yolked eggs. 11. The yolks of the multiple-yolked eggs of mature birds are not consistently smaller than the yolks of the normal eggs produced during the same period. 12. Multiple-yolked eggs are longer in proportion to their breadth than the normal eggs of the same individual. The physiological bearing of these facts is discussed.