This study and later ones have forced upon me the conclusion that these assumptions are without basis. Eggs freshly removed from the body are not in the same physiologic condition, as measured by any of the tests I have proposed. Given an originally limited variability of the eggs—for the chemico-physical explanation of which see Loeb and Chamberlain (4)—which variability I shall term the primary varia bility, further variations and types of variants are superimposed by reason of the fact that the eggs do not all ripen' at the same time within the body. Further variability is due to the fact that the eggs are subjected to the injurious influences of the body fluid for intervals varying with the time since maturation.
When such eggs are placed in sea-water the physiologically different groups of eggs are again affected very unequally.
The totality of these varying influences produces marked variations of a number of characters among the eggs of a given female, as well as the eggs of different females.
We have no direct or simple measure of the time since maturation of the egg, nor of the physiological condition of the eggs. But one can
obtain a very definite idea of the physiological condition of any sample of eggs by ascertaining the extent of certain changes in size, shape, dissolution of jelly layer, retardation of rate of membrane formation, and rate of cleavage and total cleavage, all of which, and possibly others, serve as different and corroborative indices of their physiological condition. The nature of the chemico-physical factors involved in these variations was made known from a study of aging eggs.
From this it follows that for a study of the physiology of the germ cells, or for any experimental work that involves a comparison of germ cells from different individuals, it is not sufficient to use eggs of the same chronologic age, but by actual tests, as shown above, to choose eggs of the same physiologic age—i. e., eggs most nearly in the same physiologic condition. If this be done we should expect less conflicting results than have obtained heretofore.