and the rudimentary heart commences to beat. No glycogen cells can be detected at this time, but about the beginning of the sixth day they appear as minute dark brown spots after the application of the dilute iodine solution. The glycogen cells increase in size and become more granular during the further development of the fish. At the time of the appearance of the cells the embryos are covered with a single layer of very thin flat epithelium. The intercellular substance of the epithelial cells can be easily and strikingly stained, after the application of a weak iodine solution and washing in water, by immersing the animal in a dilute aqueous solution of methylene blue for a short time. The blue staining fluid forms a dark precipitate with the iodine in the cement substance, and forms zigzag lines which delimit the cells in the clearest manner. The dark lines may be seen to cross the glycogen cells in many places, indicating that these cells are beneath the epithelial covering.

The glycogen cells are usually more or less elliptical and their dimensions vary with their stage of development. When they first appear their diameters may vary within the limits of 3μ and 10μ. At this time the protoplasm of the cells forms a ring surrounding a large central vacuole containing the glycogen granules. One part of the ring is usually thickened, and contains an elongated elliptical or crescentic nucleus. As the cells enlarge with the advanced development of the fish their vacuoles encroach on the protoplasm until the cells are converted into microscopic sacs of glycogen, in the walls of which a long elliptical or reniform nucleus can usually be found. At this stage the diameters of the cells may be 15μ to 25μ, and the granules, stained a mahogany color with iodine, are chiefly found just below the cell membrane. A number of these granules may coalesce and form a rod-shaped body in the interior of the cell. Sometimes three of the rods unite in the shape of a Y. The stained granules of glycogen dissolve with considerable rapidity in the water containing the preparation, and many of them disappear after a few minutes, leaving the thin cell membrane containing the

nucleus. A very weak solution of iodine formed by adding a drop or two of the tincture to 5 c.c. of water gives the cells their characteristic color in a few seconds if the animal has been removed from the egg envelopes. If the embryos retain their gelatinous envelope they are stained in a few minutes, and it is easy to follow the gradual staining of the cells before the animals are killed by the iodine.

At the time of the first appearance of the glycogen cells there are no blood globules in circulation, but these are first seen a day or two later. At a little later period the liver is formed, and may be stained a brick red by the iodine solution. The liver cells do not contain glycogen granules but are diffusely stained a lighter and more reddish color than the subepithelial glycogen cells.

After a certain degree of development of the fish the number of the glycogen cells becomes gradually lessened by absorption. As I have had the perch under observation for only a limited time after hatching I have never witnessed the complete disappearance of the cells. In and after the third week of development their number becomes much smaller. At that time the glycogen cells of the tail may be crowded into its edge, and those of the pectoral fins arranged in columns radiating in the direction of the striation. This change in position is probably due to the growth of other tissue elements which displace the glycogen cells. In advanced development I have noticed in the tail fin many smaller mesoblastic cells which are not stained with iodine. I have found many glycogen cells, very similar to those of the yellow perch, in recently hatched pike-perch or wall-eyed pike, and in the small-mouthed black bass, but some differences in the appearance of the cells in the different species, and in the solubility of their glycogen granules were noted. The glycogen cells of the pike-perch are coarsely granular, and their glycogen dissolves very rapidly in the dilute iodine solution. The nuclei of the cells are not so apparent as those of the yellow perch. The glycogen cells of the pike-perch may be seen under the

microscope as light spots without the iodine treatment, and an enormous number of the cells are scattered over the yolk sac. The cells of the small-mouthed black bass are large and contain much glycogen which dissolves very readily in water after iodine staining. I have noted in pike-perch which have been kept under observation for a considerable time that their glycogen cells become greatly diminished in number. I have not been successful in finding the glycogen cells in all species of fish. I have never been able to discover them in Fundulus, and have sought for them in vain in recently hatched smelt. They evidently act as temporary reservoirs of glycogen, but why they are present in some species of recently hatched fish, and not in others, is not apparent.

If it should be discovered that these peculiar cells can be isolated and satisfactorily cultivated in artificial media, they will offer most promising material for studying experimentally the formation of glycogen.

MONSON, MASS., August 23, 1920

FREDERICK W. ELLIS

THE OVARIAN CYCLE OF SWINE

MOST of our information regarding the changes in the mammalian ovary during the various events of the reproductive cycle has been gained from study of the laboratory rodents and small carnivores. The domestic ungulates, on account of their large size and commercial value, have been neglected in this respect, although they promise certain advantages because of the simplicity of their ovarian structure and the regular, outspoken appearance of œstrus.

The only attempt to follow the history of the ripening follicles and the corpora lutea of an ungulate, with material of known history, is that recently published by Max Küpfer of Zurich, who made use of the

1 Küpfer, Max, "Beiträge zur Morphologie der weiblichen Geschlechtsorgane bei den Säugetieren,' Denksschr. d. Schweiz, Naturf. Gesellsch., 1920, Bd. LVI.

municipal abattoir of that city to procure a large series of ovaries of the cow. He was able to obtain records of the last appearance of oestrus in a certain number of animals (apparently 33) and has given a set of handsome plates illustrating the rise and retrogression of the corpus luteum. From the gross appearances and from measurements (no microscopic studies were made) Küpfer states that the intercestral period of 21 days may be divided into two parts. During the first 10-11 days after ovulation the corpus luteum is slowly reaching its full size, and thereafter it is in a state of retrogression which continues throughout the next interval, until by the time of the second following ovulation (42 days) the corpus luteum is macroscopically insignificant. The ovaries of animals undergoing uninterrupted astrus cycles will there fore contain the follicles and corpora lutea of two or three periods, at successive stages of growth and retrogression.

The present writer has been endeavoring to piece out a similar account of the pig, in order to provide an anatomical basis for the physiological relations of ovary, ovum, and uterus in this species, and has published a description of the mature follicles and developing corpora lutea up to the tenth or eleventh day, but has been unable, until the present, on account of conditions of the meatpacking trade, to follow the animals longer than this time. The lacking material has now been supplied, through the cooperation of Mr. W. N. Cooper, manager of the American Feeding Company of Baltimore, at whose large piggery farm a series of 22 sows has been obtained covering practically every day of the 21-day cycle.

The story as read from these specimens is a simple one, as will be seen from the accompanying diagram. It appears that mature ovaries of non-pregnant animals contain a reserve stock of follicles of 5 mm. diameter or

2 Corner, G. W., "On the origin of the corpus luteum of the sow from both granulosa and theea interna, Amer. Jour. Anat., 1920, Vol. 26, pp.

117-183.

less. One or two days before the onset of œstrus some of the follicles rapidly enlarge to the full diameter of 7 to 10 mm., and the enclosed ova pass through the preliminary stages of maturation. Ovulation occurs on the second of the three days of oestrus; the ova are three days en route through the Fallopian tube and pass into the uterus on the fourth day. If not fertilized they degenerate in utero about the seventh or eighth day after ovulation. The corpora lutea, as already described, reach full histological complexity about the seventh day, by which time

When the pig's ova are fertilized, the embryos gain attachment to the uterine wall between the tenth and fifteenth day after ovulation. It is a most important fact, therefore, that the corpus luteum persists until the fourteenth or fifteenth day, for this finding harmonizes with the current hypothesis that the corpus luteum exercises an effect upon the uterus, preparing it for implantation. The duration of the corpus luteum is quite variable in different species, but in none has it been found less than the time required for attachment of the embryos. Another sup

oestrus

2.

no

DAYS O

they have attained a diameter of 9 mm. The new specimens show that they remain in a state of full development, without obvious further change, until the fourteenth or fifteenth day after discharge of the follicles, and then begin a retrogression which is initiated by a sudden disintegration of the granulosa lutein cells, which have formed the chief bulk of the organ. In a few days more the corpora consist only of connective tissue containing in its meshes a few lipoid-laden cells; and by the time of the next ovulation they have diminished in size to a diameter of 6 mm. During the second intercestral interval after their formation they shrink still further, until at the age of 40 days they are but 2 or 2.5 mm. in diameter. After this they are not readily distinguishable from other ovarian tissues in the gross, and microscopically are so far degenerated that one does not feel able to separate them from atretic follicles.

position with regard to the function of the corpus luteum, that it serves, while present, to restrain the growth of follicles, is also borne out by our observations, as far as they go, for it will be noticed that a new group of follicles passes beyond the resting dimension only after the degeneration of the last corpora is under way.

A full account of these studies will form part of a monograph on cyclic changes in the ovaries and uterus of the pig, now in preparation.

GEORGE W. CORNER JOHNS HOPKINS MEDICAL SCHOOL

THE NATIONAL ACADEMY OF

SCIENCES

THE annual meeting of the National Academy of Sciences was held at the Natural History Building, U. S. National Museum, in Washington on April 25, 26 and 27, 1921.

The quantum law and the Doppler effect: WILLIAM DUANE.

Preliminary measurements of the effect of high pressures on the thermal conductivities of liquids (illustrated): P. W. BRIDGMAN.

The stratification of suspended particles (illustrated): C. E. MENDENHALL and MAX MASON. Transmission characteristics of the submarine cable (illustrated): J. R. CARSON and J. J. GILBERT (introduced by J. J. Carty and F. B. Jewett).

Radiation from transmission lines: J. R. CARSON

(introduced by J. J. Carty and F. B. Jewett). Application of the principle of similitude to the hydraulic problem of the surge chamber (illustrated): W. F. DURAND.

Theories of osmotic pressure; Comments on the Borelius space-lattice theory of the metallic state: E. H. HALL.

Metamorphism in meteorites (illustrated): G. P. MERRILL (introduced by Whitman Cross).

The Island of Tagula (New Guinea), its satellites and coral reefs; The shallow seas of Australasia: W. M. DAVIS.

On the radiation of energy from coils in wireless telegraphy; On the vibrations of gun-barrels; On the problem of steering an automobile around a corner: A. G. WEBSTER.

Evening Session

Address by His Serene Highness Albert I., Prince of Monaco, Agassiz medalist, Auditorium U. S. National Museum. Reception to the Prince, Galleries, U. S. National Museum.

TUESDAY, APRIL 26 Morning Session

A model of the solar gravitational field: EDWARD KASNER.

On the problem of three or more bodies: GEORGE D. BIRKHOFF.

Quaternions and their generalizations: L. E. DICKSON.

Investigations in algebra and number theory: L. E. DICKSON.

On the approximate solutions in integers of a set of linear equations: H. F. BLICHFELDT. A provisional theory of new stars: H. N. RUSSELL, The compilation of star catalogues by means of a doublet camera (illustrated): F. SCHLESINGER. The National Research Council: VERNON KELLOGG. The order of the stars (illustrated): W. S. ADAMS. Cooking with solar heat on Mt. Wilson (illustrated): C. G. ABBOT.

The evolution of matter: F. W. CLARKE.

The differences between variable series: FRANZ BOAS.

Life of James Hall, of Albany, geologist and paleontologist, 1811-1890 (by title): J. M. CLARKE,

Afternoon Session

The classification of animals: AUSTIN H. CLARK. Attempts to acclimatize Aphelinus mali in France, South Africa, New Zealand and Uruguay (illustrated): L. O. HOWARD.

Note on structure of the trilobite (illustrated): C. D. WALCOTT.

Origin and history of the Ursidae or bears in the Western Hemisphere, with particular reference to the bearing of this question on problems of geographical history (illustrated): J. C. MER

RIAM.

The evolution, phylogeny and classification of the Proboscidea (illustrated): H. F. OSBORN. Experiments in epidemiology: SIMON FLEXNER. Effect of administering various simple metabolites upon the heat production of the dog (illustrated): GRAHAM LUSK.

The physical and chemical behavior of proteins (illustrated): JACQUES LOEB.

The skin temperature of Pachyderms (illustrated): FRANCIS G. BENEDICT, EDWARD L. Fox and MARION L. BAKER.

The temperature factor in phytopathology (illustrated): L. R. JONES.

Results of feeding experiments with mixtures of
food stuffs in unusual proportions (illustrated):
T. B. OSBORNE and L. B. MENDEL.
Population (illustrated): C. B. DAVENPORT.
Measuring higher grades of intelligence: E. L
THORNDIKE.

A study of specific forces of mortality: RAYMOND
PEARL and CHARMIAN HOWELL.

SMITHSONIAN INSTITUTION, WASHINGTON

C. G. ABBOT, Home Secretary

THE EQUILIBRIUM FUNCTIONS OF
THE INTERNAL EAR1

In this paper I have not attempted to survey the whole range of present-day problems on the functions of the labyrinth but have confined myself to some phases of two fundamental questions. (1) What and how much differentiation of function can be proved to exist in the different labryinthine structures concerned in equilibrium? (2) How does movement or change of position of the body give rise to the excitation process in the labyrinth?

I wish to state at the outset that merely for the sake of brevity specific mention will not be made of the reasons for assigning the functions discussed to the inner ear rather than to the movement of retinal images or to other sources of sensory stimuli, but must have it understood that those possible errors have not been left uncontrolled. Furthermore I have dealt with the phenomena objectively, because the experimental work which can throw light on these questions has necessarily been done upon animals in which the postulation of subjective sensations is unsafe or unnecessary. Furthermore I have not been unmindful of the fact that the reactions in the form of compensatory movements and forced positions include the simultaneous activity of many muscle groups, but I have used the compensatory movements of the eyes as the most convenient index of the labyrinthine reflexes, and also as the simplest to describe.

The labyrinth of the higher vertebrates must be used in the solution of many yet unsolved problems, but for the two fundamental questions now before us it presents insuperable difficulties. On the other hand the ears

1 Read before a joint session of the American Society of Naturalists and American Society of Zoologists, December 30, 1920.