THE DEVELOPMENT OP THE CORPUS LUTEUM. 189

The Development of the Corpus Luteum:a Review.

ByFrancis H. A. Marshall, ITI.A., D.Sc,

Carnegie Fellow, University of Edinburgh.(From the Physiological Laboratory of the University of Edinburgh.)

THE present paper is the result of an attempt to collecttogether and give an account of the literature of the for-mation of the corpus luteuni, during the last ten years, thatis, since the publication of Sobotta's first paper on the corpusluteum of the mouse.

Of the three original hypotheses pub forward to explain themode of formation of the corpus luteum, and the origin of thelutein cells, that of Paterson, who regarded the structure asderived from the blood coagulum left in the cavity of theGraafian follicle after its discharge, gained few or no ad-herents among subsequent investigators. The other twotheories, those of von Baer and Bischoff, on the other hand,have each received a considerable amount of support. VonBaer supposed the corpus luteum to be a connective-tissuestructure, in the formation of which the membrana granulosaor follicular epithelium had no share; while Bischoff con-cluded that the lutein cells were formed by the hypertrophyof the epithelial cells of the undischarged follicle. Amongthe principal supporters of von Baer's view appear the namesof Leuckart, His, Kolliker, Slavjansky, Gegenbaur, Benckiser,Schottlander, and Minot. Those who have adopted thealternative theory of Bischoff include Pfliiger, Waldeyer, Calland Exner, Beigel, and Schulin.

190 FBANOIS H. A. MARSHALL.

The first really systematic effort to deal with the questionwas made by Sobotta, whose eai-liest paper on the subject waspublished in the ' Anatomischer Auzeiger' in 1895. In thefollowing year the complete paper was issued. These papersdescribe an investigation on the development of the corpusluteum in the mouse, in which a large series of stages wasexamined, each of them being collected according to a definiteplan, the animals being killed at known intervals after theoccurrence of coition, in reference to which the period ofovulation had been previously determined. Sobotta's in-vestigation resulted in confirming Bischoff's view that thelntein cells are the much hypertrophied epithelial cells of theundischarged follicle, the connective-tissue element whichforms an anastomosis among the lutein cells being derivedfrom the inner layer of the theca. The theca esterna isdescribed as taking no share in the ingrowth, while the thecainterna is stated to become entirely used up in the formationof the interepithelial network. The hypertrophy of theepithelial cells is described as being of the nature of asimple enlargement, unaccompanied by cell division. Thecavity of the follicle is said to become eventually filled up bya central plug of connective tissue.

The conclusions reached by Sobotta regarding the for-mation of the corpus luteum were subsequently corroboratedby him in an investigation on the corpus luteum of the rabbit,the stages of development being also obtained by killing theanimals at stated intervals after coition.

In 1898 Stratz published descriptions of stages in. the for-mation of the corpus luteum of Tars ius , Tupaia, andSo r e x ; and these agree in all essential particulars with theaccounts given by Sobotta.

The development of the rabbit's corpus luteum was alsostudied by Honore, who adopted the same method as thatemployed by Sobotta. According to Honore the inter-epithelial proliferation of connective tissue is derived in partfrom the theca externa, and not exclusively from the innertheca, as supposed by Sobotta; while the theca interna is

THE DEVELOPMENT OF THE CORPUS LUTEUM. . 191

stated to be not entirely exhausted by the ingrowth, some.part remaining to form a layer within the outer theca, afterthe.full formation of the corpus luteum.

Kreis's observations on the young human corpus Inteumlikewise support the hypothesis put forward by Bischoff.

.Belloy, who investigated the formation of the corpus luteumin the rat and guinea-pig, while regarding the lutein cells as

• being derived from the follicular epithelium, describes anactive proliferation of these cells soon after the follicle'srupture. No figures are given by Belloy, and it seemspossible that he has confused the ingrowing cells of con-nective tissue from the theca interna with the membranagranulosa cells. Bouin, who also investigated the corpusluteum of the ra.t and guinea-pig, reached conclusions similarto those of Belloy.

Heape, without entei'ing into a discussion on the origin ofthe lutein cells, lays some stress on the absence of diyisionamong these cells in the ovaries of certain monkeys, pointing

-out that the enlargement is the result of a simple hyper-trophy.

Babl, writing especially on the human corpus luteum, con-cludes that the lutein cells have a double origin, arising bothfrom the membrana granulosa and from the theca interna.

A number of investigators, on the other hand, since thepublication o£ Sobotta's work, have adopted the theoryoi'iginally put forward by von Baer, that the lutein cells arisefrom the connective-tissue wall, the follicular epitheliumbeing either completely discharged along with the ovum andthe greater part of the liquor folliculi, or else being partiallydischarged and partially degenerating in situ. Among thoseholding this view are His, Kolliker, and Paladino, who havelately reiterated their former opinions.

Von Baer's theory has also received considerable supportin recent years from Nagel, who has described the corpusluteum in the human subject as an entirely connective-tissuestructure. In this he has been followed by Clark, who worked

.on the formation of the corpus luteum in the sow. and in .the

192 FJUNG1S H. A. MARSHALL.

human female, and claimed that the result of his investigationhad put the matter almost beyond question. Clark's accounthas been confirmed by Doering, who also worked upon thesow's corpus luteum. Others who have adopted the viewthat the luteiu cells have a connective-tissue origin areBiihler, Wendeler, and Stockel, who have examined anddescribed developing human corpora lutea.

None of these investigators, however, appear to liave givenan account of the growing corpus luteum in all stages ofdevelopment, while in the case of several of the accounts, it isnot clear that the structures described were not in realityatretic follicles, that is to say, follicles which had undergonedegenerative changes without discharging their ova. On theother hand, the words used in a description by Clark point tothe conclusion that this author was dealing with the degenerateepithelial cells of an atretic follicle. It seems not improbablethat the young human " corpus luteum" which Doeringdescribes was also an undischarged atretic follicle; whileKolliker's opinion that the corpus luteum is a connective-tissue structure appears to he founded on the assumptionthat the changes undergone by discharged follicles andretrogressive undischarged or atretic follicles are identical incharacter. His, and also Biihler, with reference especially toSobotta's work on the mouse, have remarked that it canscarcely be au accidental circumstance that the accountsgiven of the development of the corpus luteum in the largeranimals and in man are radically different from those describedfor the smaller species. That the discrepancy between theaccounts of various investigators depends upon the size ofthe animals employed does not seem, on the face of it, a veryprobable suggestion. It is to be noted further that in theinvestigations of all these writers who have upheld theconnective-tissue theory the ages of the developing corporalutea were unknown, the material in no case being obtainedby Sobotta's method of killing the animals at definite intervalsafter coition.

In 1901 the present writer published a preliminary account

THE DEVELOPMENT OF THE CORPOS LUTEUM. 193

of an experimental inquiry upon the formation of the corpusluteum in the sheep. In this inquiry the sheep were killedat stated periods either after coition or after the animals hadbeen observed to undergo oestrus. The relation which wasfound to exist between the condition of development of thecorpus luteum and the leDgth of the interval that was allowedto elapse between cestrus and the killing of the animalj was initself a strong presumption that ovulation in the sheep occursnormally during oestrus. Thus the approximate age of theyoung corpus luteum or discharged follicle could in everycase be determined. The result of this investigation was toconfirm in all essential particulars Bischofi's theory, whichhad been accepted by Sobotta. The sheep, however, wasfound to present some differences from the mouse in regardto the mode of formation of the corpus luteum, the connectivetissue ingrowth beingderived partly from the theca externa, andnot merely from the theca interna, and the follicular epitheliumcontinuing to undergo division after the rupture of the follicle,but with greatly decreased frequency. The former of thesetwo observations is in agreement with Honore's statement inregard to the interepithelial connective tissue in the rabbit.The theca interna was said to become entirely used up in theformation of the connective-tissue ingrowth, this statementagreeing with Sobotta's description, but differing from thatof Honore. Two years later the complete account of thedevelopment of the corpus luteum in the sheep was published.

The description given in these papers is thus completelyopposed to His's suggestion that the mode of formation ofthe corpus luteum in the larger mammals is different fromwhat it is in small animals like the mouse and rabbit, unless,as Sobotta remarks, it was intended to include only the ele-phant and the whale in the former category.

Meanwhile, in 1901, the same year in which the preliminaryaccount referred to above was issued, van der Stricht pub-lished descriptions of the developing corpus luteum of batsbelonging to the genera Vespe rugo , V e s p e r t i l i o , andPlaco tus . This author's researches also resulted in eon-

194 FRANCIS H. A. MARSHALL.

firming Bischoff's hypothesis, but he differs from others whohold this view in stating that a certain relatively small numberof lutein cells arise from interstitial cells existing in the innertheca of the connective-tissue sheath. Van der Strichtdiffers from Sobotta, while agreeing with the preseut writerin finding mitotic division among the follicular epithelial cellsafter the follicle's rupture. A figure is given iu one of vander Stricht's papers of a section of a human ovary in whichsuch division is also shown to exist. It would thus appearthat the lutein cells, at any rate, in.certain mammals, do notarise entirely by simple hypertrophy of the follicular epithelialcells, but by hypertrophy accompanied by a greater or lessamount of cell division. The very early appearance of fattyparticles in these cells in the bat's discharged follicle is apoint of considerable interest to which van der Stricht callsattention.

At the meeting of the " Anatomische Geselischaft" atBonn, Kopsch exhibited sections of corpora lutea from thesow, representing three-, six-, and ten-day stages of develop-ment. These preparations in a general way supported thefollicular epithelial theory.1

Sobotta's account of the formation of the corpus luteum inthe rabbit has been recently further confirmed by Cohn, whoalso obtained a series of stages by killing the rabbits at statedperiods after copulation. Thus the development of therabbit's corpus luteum has formed the subject of experimentalinvestigations by three separate observers—Sobotta, Honore,and Cohn,—who have all arrived at the conclusion that thelutein cells are hypertrophied follicular epithelial cells.

An important paper on the corpus luteum of the " Marsupialcat," Dasyurus v iver r inns , by Sandes shows that thisstructure is formed in a similar way in marsupials to what itis in the Eutheria. The theca interna folliculi is shown to berudimentary in Dasyurus. Owing to this circumstance Sandespoints out that it is easier to follow the subsequent changes

1 Vide Sobotta, Merkel and Bonnet's 'Ergebnisse d. Anat. u. Entwick.,'vol. xi, 1902.

THE DEVELOPMENT OF THE CORPUS LUTEUM. 195

undergone by this layer dui'ing the formation of the corpusluteum than in certain of the other mammals. Biihler hadsusrafested that Sobotta might have confused the cells of thetheca interna during an early stage of ingrowth with thosebelonging to the follicular epithelium, which they undoubt-edly at one period resemble, saying that the latter authorhad not properly described the connective tissue sproutinginto the cavity of the newly-discharged follicle. Sandes's•description is of value as showing that Biihler's criticism losesall force when applied to Dasyurus , with which the mem-brana granulosa undergoes so considerable a hypertrophyprior to the thecal ingrowth as to sometimes almost fill thecavity of the follicle, and thus all possibility of a confusionbetween epithelial and connective-tissue cells is precluded.

Sandes describes also the fate of those follicles which donot rupture in Dasyurus . In the case of the smaller folliclesboth follicular epithelium and ovum frequently degenerate,but the former may persist as a single layer of cuboidal epi-thelium. Sometimes a metaplasia of epithelial cells intospindle- or star-shaped cells is said to take place, as in otheranimals. In this way the cavity of the follicle becomes filledup, or it may be obliterated by the ingrowth of connectivetissue. Other atretic follicles may for a time remain cystic,with a layer of cuboidal epithelial cells, which eventually dis-appear. Follicles which have become ripe, or almost ripe,however, are stated to pass through changes precisely similarto those undergone by corpora lutea, except that the ovum,instead of being extruded, degenerates in situ, becominginvaded by leucocytes and by connective tissue.

The corpus luteum in the marmot (Spermophi luscitillus) has been shown by Vb'lker to be formed in essentiallythe same way as that of the mouse, the rabbit, and the sheep.It resembles that of the sheep and (according to Honore'sdescription) that of the rabbit, in the fact that the thecal iu-growth is not merely confined to strands of tissue arisingfrom the inner layer. It also resembles the rabbit's corpusluteum (according to Honore) iu that the theca interna need

196 FRANCIS H. A. MARSHALL.

not become entirely spent in the formation of the inter-epithelial connective tissue. Volker finds also in unrupturedatretic follicles lutein cells which are similar to those ofdischarged follicles.

Two authors who have recently written on the formation ofthe corpus luteum reject Bischoff's theory, on what substantialgrouuds I find it difficult to understand. Of these, Jankowskybases liis opinions on the study of a miscellaneous collectionof material obtained mostly from the sow, but without anyattempt at systematic investigation. The few figures whichthis author gives do nob seem to me in any way opposedto the follicular epithelial theory, while the figure of thedeveloping corpus luteum from the guinea-pig appears ratherto support the hypothesis that the hypei'trophied cells arisefrom the membrana granulosa, and the anastomosis betweenthose cells from the tissue of the theca. Jankowsky's view islargely based on the appearance of " lutein cells " in the thecainterna prior to the rupture of the follicle.

Williams, in a recent work on obstetrics, takes up thesame position as Jankowsky, partly on the ground that " themembrana granulosa presents extensive degenerative changes,and is usually cast off in great part at the time of rupture,"and partly because the cells of the theca interna undergomarked changes during the follicle's development, andeventually come to resemble lutein cells. The former state-ment, indeed, is very far from being proved, while the latterappears to me to be singularly inconclusive. Williamsargues also that the degenerative changes which have beenobserved in the epithelium of atretic follicles afford evidencethat similar changes occur in discharged follicles. "Obser-vations based upon the study of several hundred human1

corpora lutea have convinced me that the connective tissueorigin of the lutein cells is established beyond all reasonabledoubt." Williams, however, does not say that these speci-mens have been described in any published paper, and, inthe absence of the evidence, I am unable to regard hisopinion as in any way conclusive.

THE DEVELOPMENT OF THE CORPUS LUTEUM. 197

The changes undergone by the discharged follicle havealso been studied in various lower vertebrates. J3iihler,who investigated the ovaries of Cyclostomes and certainTeleosteans, was unable to find any hypertrophy of thefollicular wall, and Cunningham arrived at a similar con-clusion for the spent follicles of Teleosteans. The presentwriter has examined the discharged follicle of the commonfowl without being able to detect any hypertrophy of thefollicular epithelium. On the other hand, Mingazzini hasdiscovered such hypertrophy in certain reptiles, structuresresembling mammalian corpora lutea being found to occur;while Giacoraini, who has investigated the subject in birds,amphibians, and, more particularly, in elasmobranch fishes,also gives an account of the formation of corpora lutea bythe hypertrophy of the follicular epithelium. The latterauthor describes and figures the corpus luteum of Mylio-ba t i s as a glandular body in which the follicular epitheliumis penetrated by an extensive ingrowth of connective tissueand blood-vessels. This account agrees substantially withwhat is found to take place in the mouse, the rabbit, and thesheep. A similar description is given by Wallace of thespent follicles in the fishes Zoarces and Spinax. Zoarces,however, presents a comparatively slight resemblance to themammals in regard to this point, there being merely a slighthypertrophy of the follicular epithelial cells. In Spinax>on the other hand, there is a considerable hypertrophicenlargement of these cells, together with a thecal ingrowthat various points in a radial manner, and an ingrowth ofblood-vessels. LuceiD has also described corpora lutea inthe reptiles Anguis and Seps, with which there is a simplehypertrophy of the cells of the follicular epithelium, un-accompanied by ruitotic division.

It thus appears that the follicular epithelial theory of theorigin of the corpus luteum of mammals has been found tobe true also for various members of the other vertebrategroups.

The chief results obtained by the investigations of Sobotta,

198 FBANCIS H.A. MARSHALL. '

Strata, Honore, van der Stricht, Colin, Sandes, Volker, andthe present writer, all of whom agree in adopting this theory,may be summarised as follows :

The lutein cells of the fully-developed corpus luteumrepresent the epithelial cells of the undischarged Graafianfollicle. These cells, after rupture, undergo an enormoushypertrophy, which may be accompanied in the earlier stagesby mitoti.c division, but usually only to a relatively slightextent (Ovis, Vesperugo, etc.). Meanwhile, the thicknessof the wall of the developing corpus luteum is further increasedby an ingrowth of connective tissue from the side of thefollicle, forming eventually an anastomosis of cells, generallyfusiform in shape, between the hypertrophying follicularepithelial cells. This connective tissue is derived eitherfrom the theca interna alone (Mus, Tars ius , Tupaia,Sorex, Dasyurus , Vesperugo, etc.), or it may arise fromboth theca interna and externa (Lepus, Ovis, Spermo-philus). The formation of the anastomosis is accompaniedby an ingrowth of blood-vessels, which gradually increase innumber throughout the young corpus luteum. The thecainfcerna may become entirely spent in this process (Mus,Tars ius , Tupaia, Sorex, Ovis, Dasyurus) , or certainstrands of this layer may remain outside the hypertrophiedepithelial cells after the complete formation of the corpusluteum (Lepus, Spermopli i lns , Vesperugo, etc.). Cer-tain cells in this layer are stated in some cases to become trans-formed iuto lutein cells (Vesperugo, etc.). The cavity ofthe discharged follicle becomes completely filled in eventuallyby the further growth inward of connective tissue accom-panied by blood-vessels.

The corpus luteum may attain to very great dimensions,this structure, when fully formed, in the cow, having adiameter of from two to three centimetres, according toSchmidt.1 Its large size is all the more remarkable in view

1 Schmidt's paper, besides containing observations on the corpora lutea, liasalso an interesting account of the variation noted in the duration of thecestrous cycle, or the interval between two successive "heat" periods, in

THE DEVELOPMENT OF THE CORPUS LUTEUM. 199

of its resulting fco a large extent from the simple hypertrophyof certain of its constituent cells, namely, those which com-prised the epithelium of the ripe follicle. The wonderfulproperty which these cells possess of enlarging within a veryshort time of the follicle's rupture, a rapidity which seems tobe especially marked in the case of the sheep's corpus luteum,is apparently without parallel in the histology of the Verte-brata. This unique characteristic becomes additionally in-teresting when considered in relation to Pfluger's hypothesis,since supported by Schafer and others, that the cells of thefollicular epithelium have a totally different origin fromthose belonging to the thecal tissue, being in f;ict derivedfrom the same group of cells as that from which tlie ovaarise.

POSTSCRIPT.

Heape, in a recently published paper, describes the forma-tion of the corpus luteum in the rabbit as follows:—"Thecorpus luteum is formed by the ingrowth of cells surround-ing the follicle together with the follicular epithelium; theingrowth being at one time apparently a forcible rush beforewhich the loosened epithelium is driven. The ingrowthtakes place in the first instance in the region of the base ofthe follicle."

Miss Lane-Olaypon, in a paper lately communicated to thePhysiological Society, " On the Post-Natal Formation ofPrimordial Ova," states that the ovarian interstitial cells, andthe follicular epithelial cells, like the primordial ova, are all" derived from the original ingrowths of the germinal epithe-

cattle, as deduced from the study of 500 cases. The most usual length ofthis period appears to be twenty-one days, but the variation was found torange from six days to one hundred and twenty-one, or even more days. Allvariations between these periods were noted to occur. Schmidt's observa-tions are in direct opposition to Beard's speculation regarding the " Span ofGestation and the Cause of Birth " (Jena, 1897), according to which theinterval between two " heat " periods is assumed to bear a fixed relation tothe length of the gestation period.

VOL. 49, PART 1.—NJfiW SERIES. 15

200 FRANCIS H. A. MARSHALL.

Hum," and not " from the mesoblast, which gives rise to the

connective tissue and blood-vessels." If the epithelial and

interstitial cells are potentially and by origin identical, this

fact helps to elucidate Van der Strieht's discovery that in

the bat's ovary both of these elements may take part in the

formation of the lutein cells. It is possible also that it pro-

vides an explanation of some of the discrepancies between

statements by various authors regarding the mode of de-

velopment of the corpus luteum in different animals. Miss

Lane-Claypon says that in the rabbit "the interstitial cells form

by far the largest part of the adult ovary," while in the

sheep, judging by my own observations, they are relatively

scarce. F. H. A. M.

September 28th, 1905.

LITERATURE SINCE THE YEAR 1895.

BELLOT.—" Recherohes sur l'origine des corps jaune de l'ovaire chez le rat etle coclion d'Inde," ' C. R. de l'Assoc. des Anatomistes,' premiere session,Paris, 1899.

BOUIN.—" Atreae des follicules de la Graaf et la formation de faux corpsjaunes," 'Bibl. Anat.,' 1S99.

BiiHLER.—" Eutwickelungsstadien menschlicher Corpora lutea," 'Verliand.d.

Auat. Gesellschaft in Pavia,' 1900.

BUHLER. —" Ruckbildung der Eifollikel bei Wirbelthieren," 'Morphol. Jabr.,'

vol. xxx, 1902.

CL4.UK.—"Urspruug, Wacbstum und Ende des Corpus luteum, etc.," ' Arch.f. Anat. u. Phys., Anat. Abtli.,' 1898; American translation in 'JohnsHopkins Hospital Reports,' vol. vii, 1899.

COIIN.—" Zur Histologie und Histogenesis des Corpus luteum und des inter-stitiellen Ovarialgewebes," 'Arch. f. Mikr. Anat.,' vol. Ixii, 1903.

CUNNINGHAM.—" On the Histology of the Ovary and of the Ovarian Ova incertain Marine Fishes," ' Q. J. M. S.,' vol. xl, 1897.

DOEBING.—"Beitrag zur Streitfrage iiber die Bildung des Corpus luteum,"

'Anat. Anz.,' vol. xvi, 1899.

GIACOMINI.—" Contributo all'istologia dell'ovario dei Selaci," 'RicercaveLaboratoria di Anatomia normale della Roy. Universita di Roma,' vol. v1896.

THE DEVELOPMENT OP THE COEPUS LUTBUM. 201

HEAPE.—"The Menstruation and Ovulation of Macacus rhesus,"'Phil.Trans., B,' vol. clxxxviii, 1897.

HEAPE.—" Ovulation and Degeneration of Ova in the Rabbit," ' Proc. Roy.Soc, B,' vol. lxxvi, 1905.

His.—Discussion,' Verli. d. Anat. Gesell.,' Tubingen, 1899.HONOMB.—"Reclierches sur l'Ovaire du Lapin. II. Reclierclies sur la For-

mation du Corps Jaune," 'Archives de Biologie,' vol. xvi, 1900.JANKOTVSKY.—" Beitrag zur Entstehung des Corpus luteum der Saugetiere,"

'Arch. f. Mikr. Anat.,' vol. Ixiv, 1904.KOLLIKEU.—"Ueber der Entwickelung der Graafschen Follikel," 'S. B.

phys.-med. Gesell. zur Wiirzburg,' 189S.KOLLIKEK.—"Ueber Corpora Lutea Atretica bei Saugetieren," ' Verh. d.

Anat. Gesell.,' Kiel, 1S98.

KREIS.—"Tiber Entwickelung und lluckbildung des Corpus luteum spurium

beim Menschen," ' Arch. f. Gynakol.,' vol. lviii, 1899.

LANE-CLAYPON.—" On the Post-natal Formation of Primordial Ova,1'' Proc.Phys. Soc.,' 'Journ. of Phys.,' vol. xxxii, 1905.

LUCIKN.— "Note preliminaire sur les premieres phases de la formation descorps jaune chez certains reptiles," ' C. R. de Soc. de Biol.,' vol. lv3

1903.MAESTIAXL.—"Tlie (Estrous Cycle and the Formation of the Corpus Luteum

in the Sheep," 'Phil. Trans.,'B, vol. exevi, 1903; "Preliminary Com-munication," 'Proc. R. S.,' vol. lxviii, 1901.

MINGAZZINI.—" Corpi lutei veri e Galsi da rettili," Ricerche ve Labol. di

Anat. Norm, di Roma,' vol. iii, 1893.

NAGEL.—"Die weiblichen Geschlechtsorgane," article in Bardelben's ' Hand-

buch der Anatomie des Menschen,' vol. vii, Jena, 1896.

NAGEL.—" Tiber neure Arbeiten aiif dem Gebiete der Anatomie der weiblichenGeschlechtsorgane," Merkel and Bonnet's ' Ergebnisse d. Anat. u. Ent-wickelungs,' vol. viii, 1899.

PALABINO.—"Per la dibuttata questione sulla essenza del corpo luteo,"'Anat. Anz.,'vol. xviii, 1900.

RABL.—"Beilrag zur Histologie des Eierstocks, etc.," 'Anat. Hefte,' vol.xi, 1898.

SANDES.—"The Corpus Luteum of Dasyurus viverrinus, etc.," 'Proc.Linn. Soc. of New South Wales,' vol. xxviii, 1903; abstract in ' Nature,5

August 20th, 1903.SCHMIDT.—"Beitrage zur Physiologie der Bruust beim Rinde," 'Trans.

Dissert.,' Zurich, Miinchen, 1902.

SOBOTTA.—"Tiber die Bildung des Corpus luteum bei der Maus," 'Anat.Anz.,' vol. x, 1S95.

202 FBANCIS H. A. MARSHALL.

SOBOTTA.—"Tiber die Bildung des Corpus luteum bei der Maus," ' Areb. f.Mikr. Anat.,' vol. xlvii, 1896.

SOBOTTA.—"tJber die Bildung des Corpus luteum beim Kaninchen, etc.,"

'Anat. Hefte,' vol. viii, 1897.

SOEOTTA.—"Noch-einmal zur Frage der Bildung des Corpus luteum," 'Arcli.

f. Mikr. Anat.,' vol. liii, 1898.

SOBOTTA.—" Uber die Entstelmng des Corpus luteum der Saugethiere,"Merkel and Bonnet's 'Ergebnisse der Anat. und Entwick.,' vols. viii andxi, 1899, 1902.

SOBOTTA.—"Das Wesen die Entwicklung und die Funktion des Corpusluteum," • S. B. der phyp.-med. Gesell. zur Wiirzburg,' 1904.

STOCKEL.—" Ueber die cystische Degeneration der Ovarien bei Blasenmole,etc.," ' Sep. Ausdruck aus der Festschrift fur Fritsch.'

STRATZ.—'Der Gesclilechtsreife Saugethiereierstock,' Haag, 1898.STRICUT (VAN DEE).—"La ponte ovarique et l'histogenese du corps jaune,"

'Bull, de l'Acad. Roy. de Medecine Belgique,' 1901.STRICHT (VAN DER).—"La rupture du follicule ovarique et l'histogenfese du

corps jauue," ' C. R. de l'Assoc. des Anatomistes,' 3e session, Lyon,1901.

STBICHT (VAN DER).—"Une anomalie interessante de formation du corpsjaune," Gand, 1901.

STRICHT (VAN DER).—"L'atresie ovulaire et l'atresie folliculairs du folliculede Graaf, dans l'ovaire de chauve souris," ' Verhand. d. Anat. Gesell.,Bonn,' 1901.

VOLKEE.—"Uber die Histogenese Corporis lutei bei den Ziese! (Spermo-philus citillus)," 'Bull. Internat. Acad. Sci.' (Medicine), Prague,1904.

WALLACE.—"Observations on Ovarian Ova and Follicles in certain Teleo-stean and Elasmobranch Fishes," 'Q. J. M. S.,' vol. xlvii, 1903.

WENDELER.—Martin's 'Die Krankheitcn der Eierstocke und Nebeneier-stocke.'

WILLIAMS.—'Obstetrics,' New York and London, 1901.