View source for Paper - The corpus luteum in the ovary of the chicken (1918)

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=Sex studies. X. The Corpus Luteum in the Ovary of the Chicken=

Raymond Pearl And Alice M. Boring

Six Text Figures And Nine Plates

Papers from the Biological Laboratory of the Maine Agricultural Experiment Station, No. 115.

==I. Introduction==

The corpus luteum is one of the clearly recognized sources of an internal secretion in the mammal. Various functions have been ascribed to it. Its function in connection with secondary sex characters has been discussed by Pearl and Surface ('15), with one piece of clear cut evidence. The case was that of a cow which developed cystic ovaries and took on male secondary sex characters. The ovaries were compared histologically with those of a normal cow and the two were found to resemble each other in all respects except that the cystic ovaries had no corpora lutea. The interstitial cells were the same in both so that the difference in secondary sex characters could not be attributed to them. The implication of the facts is that the corpus luteum has an inhibitory influence in the female which prevents maleness from developing and that when no corpus luteum is formed, male characters appear.


The chief difficulty with such a view has been that its application is very limited, as the corpus luteum has been supposed to be a structure occurring only among mammals. The secondary sex characters of birds are particularly pronounced and the results of ovariotomy experiments, such as those of Goodale, ('16) show the possibility of changing these characters experimentally. Also the many cases of hermaphrodite birds (to be considered in Study XI of this series), with varying degrees of maleness and femaleness indicate the presence of some sex regulating substance in birds. Is this substance entirely different from the corpus luteum probably connected with it in mammals, or is there a corpus luteum or its homologue in birds? An investigation of this question has been undertaken in this study. We consider that we have successfully demonstrated the presence of the corpus luteum in the domestic chicken. Further discussion of the bearing of this fact on the whole question of secondary sex characters will be deferred until a later paper of this series, which will unfortunately probably be delayed for some time, as one of the authors (R. P.) has been called upon by the government to turn his attention to practical problems during the war.


A careful examination of the ovary of a bird which has been actively laying shows three kinds of structures: the yolks of various .sizes indicating different stages of development, the discharged follicles in various stages of regression, and the atretic follicles or degenerating eggs of different sizes. These are all easy to identify when they are large enough to protrude far from the surface of the ovary, that is, when they are larger than 2 or 3 mm. in diameter. Under this size, it is impossible to distinguish the discharged follicle from the atretic. Both of them show a yellow or orange spot in the center. The question naturally arises whether these yellow spots are homologous in structure and origin with the mammalian corpus luteum. They never develop into a large mass like the corpus luteum of the mammal. They have the color of the spots on the cow ovary which indicate remains of old corpora lutea. In order to interpret these yellow spots, a study has been undertaken of the progressive and regressive changes in the cell structure of egg follicles in different conditions, undischarged, discharged and atretic.


The material used came chiefly from four birds, an actively laying Bantam, a Barred Plymouth Rock in the same condition, an old Compine past the laying condition, and a guinea-hen with a large ovary containing several large yolks. Material from a number of other Ijirds was used in the study of special points. These are some of the same birds used in Study IX. The ovaries were fixed in Gilson and McC'lendon. In the Barred Plymouth Rock ovary the different discharged follicles were sectioned separately and arranged in a series, according to size and consequent order of age since ovulation. After the study of this series, it was easy to judge of the condition of various follicles in pieces of the other ovaries cut at random. Various stains were tried, iron haematoxylin and Delafield's haematoxyhn for general histology and Mallory's and Mann's stains for secretion granule tests.

==II. Undischarged Follicles of the Hen's Ovary==

A study of the follicles of large undischarged oocytes shows them to consist of an epithelial layer, the granulosa, and two connective tissue layers, the inner and the outer theca folliculi (fig. 1). In the inner theca are located groups or nests of epithehal cells {I, figs. 1 and 2). They have been described by many authors, notably Ganfini, Sonnenbrodt and Poll, but have been called interstitial cells. Poll calls them Kornzellen at first, describes their collection into the internal theca and then implies their function by saying that the biological role of the theca interna in the formation of the corpus luteum still needs to be worked out. That he also confuses them with interstitial cells is shown by his statement that the theca interna fills up the atretic follicle with groups of Kornzellen, which is the same thing as an interstitial gland. These nests of cells in the bird are not anything like the usual glandular interstitial cells of the ovary in structure. They are about three times as large (compare fig. A and C). The nucleus is bigger and plumper, the cytoplasm is usually clear and vacuolated in appearance, only occasionally containing a few acidophile granules which stain with the fuchsin in Mallory's stain or the eosin in Mann's stain; while the real interstitial cells are crowded with granules. These large clear cells are seldom found alone, but are usually grouped into nests of various shapes, as already mentioned. The cytoplasm of these cells usually will not take up an acid stain. They remain strikingly clear, when the connective tissue all around them is highly colored. So great is the contrast that they show distinctly even at low magnification in a section such as figure 1. Furthermore, they are found in different parts of the ovary, mostly in the thcca interna, while the interstitial cells he in the general stroma, and especially on the periphery.




Fig. A Part of follicle of wall of medium sized oocyte in hen ovary. (X i)50.) Compare figure 2.




Fig. B Part of thoca interna of sixth discharged follicle in hen ovary, showing many vacuolated lutear cells. (X 9.50.) Compare figure 0.


Figure 3 shows several very young oocytes from the same ovary as figure 1. In these, the follicle consists only of a single layer of epithelial or granulosa cells (g). The connective tissue layers are not yet formed. But there are nests of clear cells (I) in the stroma nearby. Presumably these are included with the connective tissue when the theca interna is formed.

==III. Discharged Follicles of the Hen's Ovary==

In the largest follicles before ovulation, the three layers are stretched out very thin by the pressure of the large yolk within them. After ovulation, there is a shrinkage of the follicle walls, probably due to the elasticity of the connective tissue recoiling at the sudden release of pressure from inside. On the Barred Plymouth Rock ovary, the ripe yolk measured about 40 mm. in diameter, and the last discharged follicle measured 20 mm. in length from base to tip, while the next to last was 12 mm., and the fourth in the series was 7 mm. As this shrinkage in length takes place, the walls thicken until finally a small oval mass results having no resemblance to a hollow follicle. The ruptured place through which ovulation took place, becomes gradually closed up, by the growing together of the edges, and the filling of cells into the cavity. Sometimes this mass of cells proti-udes shghtly from the cavity at the old place of rupture, thus somewhat more resembling a miniature mammalian corpus luteum. Yellow pigment forms in the puckered edges of the follicle and also in the central mass.


The microscopic study of sections through discharged follicles of various ages shows that the increase of thickness of walls is due chiefly to a thickening of the theca interna. Figure 4 is a section of the last discharged follicle of the Barred Plymouth Rock ovary. It shows the thickened theca interna (i) and in addition the remnants of the granulosa (g). The latter seems to loosen from the follicle after ovulation, and the cells collect in masses in the cavity and degenerate.



The first subsequent discharged folHcle in the series to show any new microscopic features is the sixth (fig. 5), where there appears a marked increase in the number of nests of vacuolated cells in the theca interna (l). They are concentrated toward the cavity. The closeness of nests together may be partlj^ due to the shrinkage of the cavity after discharge of the egg. But as this does not seem sufficient to account entirely for the increase, the number must be added to either by di\dsion or migration. The fact that division plays some part in the process is proven by the observation of several mitotic spindles. The character of these cells shows better in greater magnification, as in figure 6 and figure B.

The further progress of the increase of vacuolated cells in the theca interna is shown in figure 7, a section of a discharged follicle too small to have been placed in the series as to time of discharge. Here the whole internal theca looks full of holes, due to vacuolated cells (I). The central ca\dty is nearly obliterated, almost as though the edges had been pulled up by a gathering string. There are, however, a few cells in the central cavity (p). These get in there by migi-ation from the internal theca.

Figure 13 shows the process in an atretic follicle where it is more conspicuous, but it is true to a more limited extent in the discharged follicles. The cells concerned have a speckled appearance in figiue 13 (d). They are abundant in the follicle wall, some are scattered among the yolk spheres in the central cavity and some are on the border line between the follicle wall and the cavity, indicating that the cells actually migrate into the cavity. Occasionally a very large central plug is formed which protrudes from the spot of rupture. Figure 7 shows a small plug of this kind (p).

The cavity usually becomes finally obhterated by the thickening of the internal theca and the formation of large masses of vacuolated cells from the original nests. In figure 8, the chief tissue consists of the masses in the internal theca (i). The line between the theca interna and externa is marked by the irregular spaces and blood vessels. The connective tissue in the center (c) shows where the edges of the internal theca have drawn together and obhterated the cavity.

We have traced thus far the general histological changes involved in the shrinking and lilling up of the discharged follicle. We must consider next in more detail, the cytology of these particular cells involved. Figure 2 and figure A show them in their original condition from a large undischarged follicle. We have earlier in this paper pointed out their especial characteristics in distinction to the interstitial cells. By the time they are close enough together to cause the vacuolated appearance of the whole inner part of the theca interna, the nuclei are somewhat shrunken and pushed to the side of the cell, suggesting active elaboration of secretion material (fig. 6 and fig. B). By the time the closing in of the follicle has neared completion (figs. 8 and 9), the character of the cells is decidedly modified (fig. C). The cell boundaries in any one small mass of cells are indistinguishable. The cells seem to have melted together so that the outlines of the vacuoles are the evidently visible lines rather than the cell outlines. The vacuoles also are much larger than previously. The nuclei are smaller and less regular in outline, they stain darker, in fact, they look shrunken. These figures show nicely the contrast between the cells which fill up this discharged follicle and the interstitial cells. The interstitial cells lie in the connective tissue of the external theca and of the internal theca in between the masses of transformed epithelial nest cells. They are entirely unchanged from their usual appearance. They show clearly because the granules with which they are packed stain vividly with acid stains. A homologous mass of cells from an older solidly filled follicle (fig. 10) is shown in figure 11 and figure D. Here the nuclei show still further signs of degeneration and the general network of the cytoplasm contains clumps that look like secretion material. These secretion particles are yellow in color. They look amorphous in character, and they vary greatly in size (fig. 20). They can not be fatty, for they have not dissolved in the clearing oils. They cannot be of the protein nature of the secretion granules of the interstitial cells, as they retain their distinct yellow color no matter how the preparation may be stained. They make a fine contrast with iron haematoxyhn, acid fuchsin, eosin, methyl blue, and still show their own characteristic yellow even with orange (1. The cell masses finally become nearly filled with this yellow material, some of it collecting in clumps several times larger than the degenerated nuclei.



Fig. C Masses of lutear cells from older discharged follicle, with interstitial cells lying in connective tissue between masses. (X 950.) Compare figure 9.





Fig. D Mass of lutear cells from discharged hen follicle, with pigment particles developed in the network. (X 950.) Compare figure 11 and figure 20.




Further tests of the character of the cell contents in these cell masses were made with Sudan III. Hand sections were made of material in McClendon's fluid. Although these could not be cut very thin, they showed that the inner lining of the early discharged follicles contains fatty material. In an old follicle with central yellow mass the cells of the yellow mass take the red of the Sudan III, but the yellow amorphous particles show in the mid^t of the red. They can be squeezed out of broken cells and isolated from the red fatty background, showing they are still yellow, unaffected by the Sudan III, and therefore not of a fatty nature. The fatty substance indicated by the Sudan III reaction in both young and old folhcles is probably contained in the vacuoles so conspicuous in paraffin sections. The xylol would have dissolved out all the fat lea\dng the vacuoles in which it had been contained.

==IV. Degeneration of Corpus Luteum in Cow Ovary==

In order to show the significance of the yellow mass formed in the center of discharged follicles in the hen ovary, we have made a brief study of the degeneration of the corpus luteum in the cow ovary for comparison. There is an extensive literature on mammalian corpus luteum, but this deals chiefly ^vith the development and early involution. Now the bird quite evidently has no structure similar to the large corpus luteum which fills up half the ovary of a cow at its full development. The small yellow spot on the bird ovary resembles the small yellow spots on the cow ovary which mark the old remains of former corpora lutea. Ovulation in the cow alternates between the two ovaries. So by studying the two largest corpora lutea on both ovaries we can arrange a series of four involution stages. Beyond that, they all seem equally shrunken and therefore can not be arranged in a further series. Such a series of four involution stages has been studied for two cows, and in addition several older corpus luteum remains.


The last formed corpus luteum is of a salmon pink color, due to a combination of the blood color and the lutein color. Sections show it composed of large plump cells with rounded nuclei, as described by Corner. These luteum cells are scattered in the midst of an areolar connective tissue groundwork (fig. 18 and fig. E). In dehydrating for embedding, the absolute alcohol and xylol become very yellow, indicating that the cells contain something soluble in these reagents. This is of course one chemical character of lutein.




Fig. E Cells from youngest corpus luteum of cow. (X 950.) Compare figure 18.

Fig. F Cells from older corpus luteum of cow, showing pigment developed in cells. (X 950.) Compare figure 19 and figure 21.



The next to last corpus luteum is much reduced in size. Its color has lost the pinkish shade and it appears a solid bright yellow. This is also soluble in absolute alcohol and xylol as in the first stage. The cells and nuclei both look a little shrunken. In one cow, this second corpus luteum contained a few amorphous yellow particles like those described foi the hen.


1n the third oldest corpus luteum, the tissue is shrunken so that a mere speck shows on the surface. This is the stage resembhng the yellow spots of the hen's ovary. Dissection shows that it is reduced in all diameters. That part of this decrease in size is due to cell shrinkage is well demonstrated by comparison of figures E and F, which are drawn to the same scale. Not only the nucleus but the cell body is at least halved in size. The color now is darker, being a brick red. This is not due to blood vessels, as sections do not show any more than formerly. It is due to the development of a dark yellow pigment, the same substance which appeared in small quantity in the younger corpus luteum and in large quantity in the hen ovary. In this stage of involution it is developed in large quantities, practically fiUing up many of the lutear cells (figs. 19 and 21 and fig. F). In unstained sections it gives a yellow color to most of the section.

In the fourth oldest corpus luteum of the two series and in the scattered older ones sectioned, the structure is similar to that in the third oldest, the yellow amorphous masses being possibly larger and more distinct.

This yellow material certainly looks the same as that in the hen ovary. The chief structural difference is that it is all confined within cells with distinct cell walls in the cow, while in the bird, the cells forming it, lose their boundaries and the particles are formed in a vacuolated network with scattered shrunken nuclei (cf. figs. 20 and 21).

Sudan III reacts similarly with hand sections of formalin material from both cow and hen ovary. All four stages in the cow series take the red color showing the presence of a fatty substance in the cell. This corroborates the evidence from the solvent action of absolute alcohol and xylol. But in the third and fom-th stages, yellow amorphous pigment particles can be seen glistening in the red background. The pigment is not of fatty nature in the cow, any more than it is in the hen. In fact, this substance is so similar in the two animals, that we shall from now on speak of a corpus luteum in the hen, and call the cells forming this pigment, lutear cells.


This development of a non-fatty pigment in the mammalian lutear cells has been already described by Mulon as occuiTing in atretic follicles. He speaks of the lipocholesterine as changing over to an indelible pigment. This same substance certainly forms in the involution of the corpus luteum of a discharged follicle as shown in this present work.

It is of especial interest to find that Blair Bell's description of the corpus luteum in Ornithorhynchus, a primitive oviparous mammal, shows it very much like that in the hen. It often remains hollow, it never becomes very large. It consists chiefly of a thickened theca interna. Sometimes it becomes a solid fibrous mass. One of Bell's figures almost exactly resembles figure 4 of this paper. One would like to know whether the yellow pigment is found in Ornithorhynchus thus making its resemblance to the bird even more striking.

==V. Biochemical Character of Pigment of Corpus Luteum==

The identity of this yellow amorphous pigment in the corpus luteum remains in the ovary of the hen and of the cow has been put to chemical tests as well as morphological; first of a microchemical nature, as already partially described, and secondly by various special chemical solvents. The work of Escher and of Palmer and Eckles on animal pigments has been consulted in selecting the reagents to use.

The microchemical tests have been discussed in previous sections, but will be summarized here. Microscopical technique processes have shown the identical beha\'ior of the pigment in hen and cow. It does not dissolve in alcohol or oils. It will not stain with basic nuclear stains such as haematoxylin and Kresylviolet, or with acid counterstains, such as eosin, methyl blue, anihn blue, orange G, or with such a stain as iron haematoxyhn. Neither does it stain with the fat stain, Sudan III, although there may be much fatty material in the cell in which it lies. As normal secretion granules of a protein nature take acid stains and secretion granules of a fatty nature take Sudan III, this pigment is neither protein nor fat in composition.


A further test of its chemical nature was made by ti-ying some of the various solvents used by Escher and by Palmer. Sections were cut in paraffine and mounted on slides and then the paraffine removed b}^ xylol and the sections treated with different chemicals. This pigment is not the carotin described by Palmer, but we could not reach any conclusion as to its chemical nature, as nothing could be found to dissolve it. But the fact of the identity of this pigment in the hen and cow is proven beyond a doubt. Concentrated HCl, HNO3 and H2SO4 were tried and had no effect except that the H2SO4 turned the particles dark brown and made them even more distinct than before. For an alkali solvent, strong KOH was used; it turned the pigment bright orange but did not ehssolve it. In adeUtion to these various other solvents were tried after consultation with the chemistry department, petroleum ether, sulphuric ether, acetone, carbon bisulphide, and carbon tetrachloride, but none of these had the slightest solvent effect on the pigment. Acetone cleared the background and this made the particles stand out more sharply. Carbon bilsulphide was allowed to act for several hours, but the preparations still contained the pigment at the enei of that time in undiminished degree. We conclude that any two substances which can withstand the action of as many well known solvents of as many different properties as this list includes must be of very similar chemical nature. This gives us one more proof that the yellow particles in the hen ovary are the same as those in involuted mammalian corpora lutea.

VI. Changes in Atretic Follicles in the Hen's Ovary==

Among the developing yolks and discharged follicles of the hen ovary are many degenerating eggs. They can be distinguish d from developing eggs by the shrunken appearance as though the contents did not ejuite fill out the foUicle. Eggs may start to degenerate at different stages. Tbe largest one on the Barred Plymouth Rock ovary was 12 mm. in diameter. Many of them show dark spots which are masses of coagulated blood. Mostly they are smaller than this when involution begins. The degree of shrinkage shows whether the involution process had recently begun or not. When these degenerating eggs are cut open, the contents is found to be in a more or less fluid state. When these atretic follicles have become reduced in size to 2 or 3 mm., it is no longer possible to distinguish them externally from the discharged follicles; the same kind of a yellow pigment appears in the center.

Studied microscopically, the chief difference between atretic and discharged follicles is that the former have a more distinct cavity which becomes obliterated chiefly by migration of lutear cells into it instead of by shrinkage of the walls. The granulosa is shed similarly. There must frequently be hemorrhage as corpuscles are often found ia the cavity. The varying quantity of yolk spheres is one indication of the degree of involution, also the number of lutear cells in the cavity. Figure 12 is an atretic follicle with considerable yolk still unabsorbed. A few lutear cells have filled in to the cavity (fig. 13, 1). It is particularly clear here that the cells inside of the inner mar^n of the theca interna are the same in structure as those of epithelial nature in the interna theca. This is just as Benthin describes it for the atretic mammalian follicles. Figures 14 and

15 show a later stage where the yolk is almost all absorbed and the ca\dty is filled with lutear cells.

Not until the cavity is filled with lutear cells does the yellow pigment already described in discharged follicles, make its appearance. It forms in the lutear cells of atretic follicles in a similar way to that in the discharged follicle. The cell boundaries are possibly not obliterated so completely, so that the morphological resemblance to the cow corpus luteum remains is even more striking than in the case of the discharged follicles. Figure 16 is part of an atretic follicle where the cells are filled with pigment. The amorphous character of this matedal shows in figure 17 a part of figure 16 under higher magnification.

It is of interest to notice that the lutear cells in the hen in both discharged and atretic follicles originate entirely from the theca interna. In mammals the origin of the lutear cells is a mooted question. Some authors, as Niskoubina, hold that they have a double origin, from granulosa and theca interna, while others such as B(>nthin and Hegar, claim that they all come from the theca interna. This point is perfectly clear in birds due to the ease with which one can distinguish these peculiar cells in the internal theca of undischarged follicles and follow them to the thickened mass in the center of the discharged follicles, and see them migrating out into the cavity of the atretic follicles.

The formation of a corpus luteum in atretic as well as discharged follicles makes it possible to identify ovarian tissue in ovaries too abnormal to have ovulated any eggs. Most of the literature of the mammalian ovary considers the involution of the atretic follicle as something distinct from that of the discharged follicle. The mass forming in the atretic follicle is called the corpus atreticum or fibrosum in contradistinction to the corpus luteum. However, Hegar says that it is hard to tell one from the other. They are practically identical in the hen.

==VII. Summary==

We are now in a position to sum up the points proving the homology of the corpus luteum in the hen and in the cow. There has been much discussion about the origin of the corpus luteum in mammals. In the hen there is no question but that the origin is simply from the theca interna.

The course of development in the hen corpus luteum is an abbreviation or fore-shortening of that in the cow. It corresponds directly to the late involution stages of the cow corpus luteum. They both contain a yellow fatty substance, as shown by the Sudan III, absolute alcohol and xylol reactions. There develops in both a yellow amorphous pigment in the cells containing the fatty substance. This pigment is similar chemically in that it will not stain with basic or acid stains; also in that it will not dissolve in any of the usual solvents, acid alkali or oil.

In the hen, a corpus luteum forms in both discharged and atretic follicles.


==VIII. Literature Cited==

Bell, W. Blaik 1917 The sex complex. Wood and Company, New York. Bknthin, W. 1910 Ueber Follikelatresie in kindlichen Ovarien. Arch. f.

Gyniikologie, Bd. 91, p. 2.

1911 Ueber Follikelatresie in Siiugetier Ovarien. Arch. f. Gynakol ogie, Bd. 94, p. 599. BouiNT ET Ancel 1912 Sur la nature lipoidienne, d'une substance active se cretee par le corps jaune des mammifere. C. R., T. 151, p. 1391. Corner, G. W. 1915 Corpus luteum of pregnancy as it is in swine. Carnegie

Inst. Washington, 222, p. 69. DuBAissoN, H. 1906 Contribution a I'etude du vitellus. Arch, de Zool. Exp.

et Gen. T. 4. Series 5, p. 153. EscHER, H. H. 1913 Ueber den Farbstoff des Corpus Luteum. Zeitschr.

Physiol. Chem., Bd. 83, p. 198. Fraenkel, L. 1910 Neue Experimente zur Function des Corpus Luteum.

Arch. f. Gynakologie, T. 91, p. 705. Ganfini, C. 1908 Sulla strutturo e sviluppo delle cellule interstiziali dell'

ovajo. Arch, di Anat. e di Emb., S. 7, p. 373. GooDALE, H. D. 1916 Gonadectomjr in relation to the secondary sex characters of some domestic birds. Carnegie Inst. Washington, 243. Hegar, K. 1910 Studien zur Histogenese des Corpus luteum und seiner Riick bildungsproducte. Arch. f. Gynakologie, Bd. 91, p. 530. Henneguy, L. F. 1894 Recherches sur I'atresie des foUicules de Graaf chez

les mammiferes et quelques autres vertebres. Jour, de I'Anat. et

Phys., T. 30, p. 1. Miller, J. W. 1910 Die Riickbildung des Corpus luteum. Arch. f. Gynakologie, Bd. 91, p. 263. MuLON AND Jong 1913 Corps jaunes atresiques de la femme. Leur pigmentation. C. R. Soc. Biol., T. 74. NiSKOUBiNA 1909 Recherches sur la morphologie et la fonction du corps

jaune de la grossesse. Dissert, de la facultc de med. de Nancy. Palmer, L. S. and Eckles, C. H. 1914 Carotin. The principal natural yellow

pigment of milk fat. I, II, III, IV. Research Bui., nos. 9, 10, 11, 12,

Univ. of Mo., Agr. Exp. Stat. Pearl, R. and Surface, F. M. -1915 Sex Studies. VII. On the assumption

of male secondary characters by a cow with cystic degeneration of

the ovaries. Ann. Rept. Me. Agr. Expt. Stat., 1915, p. 65. Poll, H. 1911 Mischlingstudien VI: Eierstock und Ei bei fruchtbaren u.

unfruchtbaren Mischlingcn. Arch. f. Mikr. Anat., Bd. 78, II, p. 63. Sonnenbrodt 1908 Die Wachstuuisperiode der Oocyte des Huhnes. Arch.

f. Mikr. Anat., Bd. 72, p. 415.

==Plates==


DESCRIPTION OF PLATES

We wish to take this occasion to acknowledge our indebtedness to Mr. Royden Hammond for all the photomicrographs, and to Mrs. Maud DeWitt Pearl for the paintings on plate 9.

PLATE 1

EXPLANATION OF FIGURES

1 Medium sized oocyte in hen ovary (X 40), showing three layers to the follicle, the granulosa {g), theca interna ({), and theca externa (e), with nests of lutear cells in the theca interna {I).

2 Part of follicle wall in figure 1 at greater magnification (X 352). Labels the same as in figure 1.


PLATE 2



EXPLANATION OF FIGURES



3 Young oocytes in hen ovary (X 352), with follicles consisting of a single layer of granulosa (g). Nests of lutear cells in the stroma nearby (l).

4 Portion of last discharged follicle in hen with thickened theca interna(0 and granulosa (g) being sloughed off into the cavity. (X 40.)



PLATE 3



EXPLANATION OF FIGURES



5 Portion of sixth from last discharged follicle, showing large number of lutear cells (Z) in the theca interna (X 40).

6 Part of figure 5 enlarged (X 176).

7 Small discharged follicle with cavity nearly obliterated. Small plug of cells (p), filling in the cavity. Theca interna filled with masses of lutear cells H). (X 40.)


PLATE 4



EXPLANATION OF FIGURES



8 Discharged follicle with cavity completely obliterated. The chief component is masses of lutear cells (l). The connective tissue center represents original location of cavity (c). X 40.

9 Part of figure 8 at greater magnification (X 176), showing interstitial cells (i.e.) in connective tissue between lutear masses.





PLATE 5

EXPLANATION OF FIGURES

10 Later stage of solid discharged follicle, showing large development of yellow pigment in lutear masses (X 40).

11 Part of figure 10 at greater magnification (X 176), showing pigment particles.

12 Atretic follicles in hen ovary, with yolk spheres in central cavity (X -10).

13 Part of figure 12 at greater magnification (X 176). Lutear cells (/) show in theca interna and also among yolk spheres in the cavity.


PLATE 6

EXPLAXATIOX OF FIGURES

14 Later stage of atretic follicle (X 40). Only a few yolk spheres remain in cavity. Cavity is practically filled with lutear cells.

15 Part of figure 14 at greater magnification (X 176), showing lutear cells in theca interna {i), as well as the central cavity.



PLATE 7

EXPLANATION OF FKiURES

16 Atretic follicle in which the pigment particles have developed in the lutear cells (X 40).

17 Part of figure l(i (X 176).




PLATE 8

EXPLANATION OF FIGURES

18 Section of youngest corpus luteum of cow (X 176).

19 Section of older corpus luteum of cow (X 176), showing cells filled with pigment particles.



PLATE 9

EXPLANATIOX OF FIGURES

20 Section of discharged follicle of hen ovary, stained in Alallory's stain. Connective tissue = blue. Corpuscle = red. Interstitial cells = purple. Lutear pigment = yellow.

21 Section of older corpus luteum of cow, stained in Mallory's stain. Tissues colored as in figure 20.

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