Book - The Development of the Albino Rat 8

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Huber GC. The Development of the Albino Rat (Mus norvegicus albinus). (1915) J. Morphology 26(2).

Normal: Introduction | Materials and Methods | Ovulation, Maturation and Fertilization | Pronuclear Stage | Segmentation Stages | 2-ceIl stage | 4-ceIl stage | 12 to 16-ceIl stages | Summary of segmentation stages | Completion of segmentation and blastodermic vesicle formation | Blastodermic vesicle | Late stages blastodermic vesicle | Egg-cylinder formation | Late stages in egg-cylinder | Conclusions | Literature cited | Figures
Abnormal: Introduction | Half Embryos in Mammalia | Degeneration of ova at the end of segmentation | Incomplete or retarded segmentation | Abnormal segmentation cavity formation | Degeneration of ova as a result of pathologic mucosa | Imperfect development of ectodermal vesicle | Two egg-cylinders in one decidual crypt | Conclusions | Literature cited
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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Development and Differentiation of the Egg-Cylinder

The material at hand is listed in table 8.

Table 8

For the stages showing the development and differentiation of the egg-cylinder in the albino rat I am able to present a series of stages which follow one another in close succession. The figures presented are in themselves so elucidative that an extended description is obviated. The stages under consideration fall within the eighth day after the beginning of insemination, judging from the great majority of the specimens at my disposal, although two rats (Nos. 17 and .S'l) killed in the latter half of the ninth day, contained stages which are younger than nearly all of those obtained the latter half of the eighth day. I am unable to state whether this is owing to a retardation in the rate of development of the ova in rats Nos. 17 and 35, or due to an error of record. The record gives date and hour of insemination and of killing, and I have no reason to doubt its accuracy. However, the two rats in question give the only instances of marked deviation from what appears as a normal rate of development as presented by the bulk of my material. Sobotta ('11) has called attention to the difficulty of obtaining successively staged material in the mouse, and cites Kolster as contending: Man konne auf die Altersbestimmung gar nichts geben." During this stage of development the decidual crypts lodging the ova are deeper than in the preceding stage, their mesometrial portion being narrower, though they are not as yet separated from the uterine lumen. The orientation of the decidual crypts and the contained egg-cjdinders is perhaps more readily made than in slightly younger stages, though not definitely enough to insure the cutting of sections in a given plane. Sections of the egg-cylinder cut in the longitudinal plane may be obtained by cutting parallel to the plane of the mesometrium or at right angles to the same. However, it is still largely a matter of chance as to whether the sections obtained pass through the midplane or at an angle thereto.


In figure 25, there are reproduced representative sections of three germinal vesicles taken from the same uterus (rat No. 35, 8 days, 18 hours) which show three closely approximated early stages in the development of the egg-cylinder. None of these three vesicles is cut in exactly the mid-longitudinal plane; especially is this true of the ends of the vesicles. Furthermore, the antimesometrial portion of each, lower part of the figure, composed of the thin-walled parietal ectoderm, shows a certain amount of folding, so that a portion of each wall is cut en face instead of en profile. The appearances here presented by the antimesometrial portion of these vesicles is not to be confused with a 'giant cell' foi'mation of this portion of the roof of the vesicle, described by Sobotta in his earlier publications, but corrected and retracted


ill his l;il('i- foiiiiiiiinical ions. \'('sic|c A, li^ufc 2."). when coinpared with xcsiclc ( ' of fi^ui-c 21, sliows only ;i sli^^lit (lincrcncc in degree of development. Vesicle .\ is of nioi-e elon^::i1ed and of more distinc11\- cNlindrical form. \\< 1 hin-walled portion (an



Fig. 25 Longitudinal sections of blastoilcrniic vesicles of the albino rat, showing entypj' or inversion of germ layers with early stages in egg-cj'linder formation. The ectoplacental cone of each is not cut through its entire length and the lower portion ot each vesicle is slight Ij' folded. X 200. A, B, and C, rat No. 35, 8 days, 18 hours, after insemination. To fit properly into the entire series these three vesicles should be from the early hours of the seventh day after insemination. ect.pl., ectoplacental cone or Trager; ecl.n., ectodermal node; ex. eel., extraembrj^onic ectoderm, early stage of its ingrowth shown in vesicle A; p. eel., parietal or transitory ectoderm; v.enl., visceral layer of entoderm; p.ent., cells of parietal entoderm.


timesometrial portion) is longer, its cavity more extensive; this is owing to a further flattening of the cells of the parietal or transitory ectoderm. In vesicle A in the section preceding the one figured, the ectoplacental cone is thicker by about two rows of cells than in the one figured ; the section figured not passing through the center of this structure. In vesicle A, the ectodermal node, which is distinctly demarked, no longer rests against the base of the ectoplacental cone, as in C of figure 24, but has been forced farther into the cavity of the vesicle by reason of proliferation of the cells at the base of the ectoplacental cone, resulting in the formation of a nearly cylindrically formed column of compactl}^ arranged, polyhedral-shaped cells interposed between the ectodermal node and the base of the ectoplacental cone, but merging into the latter without sharp demarcation. To this mass of cells the name of extraembryonic ectoderm has been given by Widakowich. However, under this term this author includes also the cells of the ectoplacental cone. The ectodermal node is of larger size than in the slightly younger stage, C of figure 24, the result of cell proliferation. In the section sketched, three mitotic figures are evident in this structure. Its cells are of polyhedral shape, and show no definite arrangement. The ectodermal node and the extraembryonic ectoderm, to the base of the ectoplacental cone, together form a cylindric structure enclosed within a layer of visceral entoderm, which in the section figured is in part cut tangentially, and thus simulates an epithelium consisting of two layers of cells, but consisting in reality of a single layer of cells. Ectodermal node, extraembryonic ectoderm, and the layer of visceral entoderm together form a structure of cylindric shape which extends into the cavity of the vesicle for a distance about one-half its extent, forming the anlage of the egg-cylinder (Sobotta). Very few parietal entodermal cells are to be found on the inner surface of the parietal ectoderm. Vesicles B and C of figure 25 differ from that discussed under A, only to the extent to which the ectodermal node has been forced into the cavity of the vesicle owing to further growth of the extraembryonic ectoderm, to the extent that in C, the elongated egg-cylinder approaches the antimesometrial end of the cavity of the respective vesicle. Ectodermal node and extraembryonic ectoderm are at this stage distinctly demarked, though in close apposition. An indenture from the surface at the region of the union of these structures with a coiiscMiucnt iiiloldin^; of llic layer of visceral enloderni is not as a rule evident, if so, only very sli«!;htly, as to the left in H; suc'li iiifoldiii};' of t he xiscenil enloderni is not i'e^;irde(l ;is li;i\in^; s|)ecial significance, 'i'hese struct u res, ectodeiinal node and extraenihi-yonic ectoderm, are api)roi)riately i-eferi'cd to :is ectodermal cylinder hy Widakowich, and with the visceral entodeini. as constitutinji; the ess-f'.yliii^lt'i' t)f Sobotta.


Under A of figure 20 (rat No. 17, 8 days. 17 liours). there is shown a representative section of a vesicle which is onl>' very slightly older than that shown under C, figure 25. This vesicle was exposed, by teasing away, after fixation, the decidual tistue forming one side of the decidual crypt; this being done before embedding, so as to admit of orientation of its long axis. This accounts for the collapsed state of the thin wall of the vesicle and its slight folding, also for the fact that the ectoplacental cone is reflected upon itself. The egg-cylinder is cut in a very favorable longitudinal plane. In its antimesometiial i)oition. lower part of the figure, the cells of the ectodermal node now show definite arrangement in practically a single layer, with alternating nuclei. The beginning of a central cavity is evident with reference to which the cells are arranged. This cavity is the anlage of the 'Markamnionhohle' of Selenka, more appropriately known as the antimesomc^trial portion of the proamniotic cavity. The cells forming the wall of the ectodermal vesicle (Ektodermblase, Selenka), derived from the ectodermal node, may now be known as the primary embryonic ectoderm (Widakowich). The extraembryonic ectoderm in the mesometrial portion of the egg cylinder has differentiated to form a relatively long irregularly cylindric structure, continuous with the base of the ectoplacental cone, composed of irregular polyhedral cells, compactly arranged and showing as yet no definite orientation. In these cells active proliferation is evidenced by numerous mitoses. The egg-cylinder is covered by a single layer of cells of the visceral entoderm. Over the antimesometrial end of the eggcylinder, the entodermal cells now present a cubic or thick pavement form, while along the sides ofthe egg-cylinder they are of columnar form, esi)(H'ially long in the region where the primary



Fig. 26 Longitudinal sections of egg-cylinders ot the albino rat, showing the anlage of the antimesometrial and mesometrial portions of the proainniotic cavity. X 200. A, rat No. 17, 8 days, 17 hours; B and C, rat Xo. 81, 7 days, 22 hours, after insemination. A, shows the very beginning of the development of the antimesometrial portion of the proamniotic cavity developing within the ectodermal node; C shows the beginning of the proamniotic cavity developing in the extraembryonic ectoderm; ect.pl., ectoplacental cone or Trager; p.ect., parietal or transitory ectoderm; ex.ect., extraembryonic ectoderm; v.ent., visceral entoderm in B and C, the cells of this layer showing the anlage of the three zones showing absorption of maternal hemoglobin; a.niet.pr., antimesometrial portion of proamniotic cavity, developing in the ectodermal node; pr.emb.ect., primary embrj-onic ectoderm; ect.ves., ectodermal vesicle; met.pr., mesometrial portion of the proamniotic cavity, developing in the extramebryonic ectoderm.


(Miihi-yoiiic ('ctodcriii and the cxt i-aciiihi-yonic cctftdcriii meet. 'I'lie s])eoial eytomorphosis imdei'{i;()iie by the eoluiiiiuir cells of the sides of the egg-eyhnder, in contracHstinct ion to those of the antimesometrial end, will be considered in later pajijcs. The visceral layer of the entoderm extends to the base of the ectol)laeental cone, in i)ai't i)assin^ o\-ei- onto the layer of pai'ietal ectoderm. In the section fifi;ure(l, cells of the jjarietal layer of the entoderm are not evident. The ectoplacental cone has grown in length in the direction of the lumen of the uterus or the mesometrial border. In the great majority of my preparations this structure is slightly compressed from side to side, so as to be broader in a plane parallel to the long axis of the uterus. In vesicle A, it is cut at right angles to the long axis of the uterus, thus appears as much narrower than in the other two vesicles of figure 26, which were cut in a plane parallel to the plane of the mesometrium. The increase in size of the ectoplacental cone is the result of active cell proliferation. Mitotic figures to the number of one, two or three, may now be observed in nearh' every section of this structure. The parietal or transitory ectoderm, continuous with the base of the ectoplacental cone, has been reduced by this stage to a thin, practically homogeneous membrane, presenting scattered, flattened nucleated cells on its inner surface. This thin membrane is now quite firmly adherent to the wall of the decidual crypt, throughout nearly its whole extent.


Under B of figure 20 (rat No. 81, 7 days, 22 hours) there is shown a representative section of a vesicle which is slightly more advanced in development than that shown in A of this figure. The antimesometrial portion of the proamniotic cavity, the anlage of w^hich was shown in the preceding stage, is well established. Its wall, consisting of primary embryonic ectoderm is composed of a single layer of cells with nuclei in essentially the same plane. The primar}- embryonic ectoderm forms a closed vesicle (Ectodermblase, Selenka) distinctly demarked from the extraembryonic ectoderm. In this as in the preceding stage the extraembryonic ectoderm forms a long cylindrical structure continuous at its mesometrial end with the base of the ectoplacental cone. The cells are of irregular polyhedral form, compactly grouped, showing as yet no definite arrangement. Cell proliferation as evidenced by mitoses is active, amply accounting for the increase in length of this structure. The visceral entoderm encloses the long egg-cylinder as a single layer of cells and is continuous at its base with the parietal entoderm, well shown at the left of the figure. The ectoplacental cone of this vesicle is very favorabl}^ cut in a plane parallel to the long axis of the uterus. This vesicle was unusually well fixed and ma}' be regarded as showing normal relations of the thin membranous wall, derived from the parietal ectoderm, and of the egg-cylinder, which reaches quite to the antimesometrial end of the vesicle.


Vesicle C of figure 26, obtained from the same uterus as was vesicle B (rat No. 81, 7 days, 22 hours), differs from that shown under B, in that it presents the anlage of a mesometrial ])orti()n of the proanmiotic cavity. In the extraembryonic ectoderm, near its junction with the base of the ectoplacental cone, two irregular spaces may be observed. These are distinctly evident, passing through the entire section, only in the section figured. The antimesometrial portion of the egg-cylinder is not cut quite through its center, so that the primary embryonic ectoderm of the ectodermal vesicle appears as a stratified epithelium, and the antimesometrial portion of the proanmiotic cavity appears as relatively small, this owing to a slight curvature shown by this egg-cylinder. The other features presented by this vesicle are sufficiently wc^ll portrayed in the figure to obviate the necessity of further description.


In figure 27, there are shown three further stages of egg-cylinder differentiation, showing progressively older stages than shown in the preceding figure. Under A of this figure, there is reproduced a representative section of a vesicle taken from the same uterus as were vesicles B and (' of figure 20 (rat No. 81, 7 days, 22 hours). The figure is not of a single section, but is combined from two sections, superimposed so as to give correct dimensions and relations. The egg-cylinder of A of this figure differs from that shown in C of fi gure 26, in that the mesometrial portion of the proamniotic cavity, developing in the extraembryonic ectoderm, is of greater dimension. Two relatively large spaces, bordered by a single layer of cells of the extraembryonic ectoderm, are to be observed. At the junction of the extraembryonic ectoderm and the ectodermal vesicle of primary embryonic ectoderm a further space of triangular outline may be seen. The primary embryonic ectoderm is arranged in the form of an oval-shaped vesicle, forming the antimesometrial end of the egg-cylinder. Its wall is relatively thin at the region of its apposition to the extraembryonic ectoderm, just below the triangular space above mentioned. This ectodermal vesicle is peculiar in that its cavity contains the remains of four cells. A study of the series of sections shows that these cells do not represent the crest of a fold of the wall of this vesicle, since they are not nearly so distinct in preceding and succeeding sections. It may only be conjectured that during the rearrangement of the cells of the ectodermal node, resulting in the formation of the ectodermal vesicle, certain of the cells became separated from the wall and remained free in the cavity. The primary embryonic ectoderm, forming the wall of the ectodermal vesicle is readily differentiated from the extraembryonic ectoderm, both by the fairly sharp definition of the ectodermal vesicle and by reason of the fact that its cells stain somewhat more deeply than do the cells of the extraembryonic ectoderm, as also the cells of the visceral entoderm. In the egg-cylinder shown under B of figure 27 (rat No. 96, 8 days) the antimesometrial portion of the proamniotic cavity, developing in the ectodermal node, and the mesometrial portion of the proamniotic cavity, developing as several discrete spaces in the extraembryonic ectoderm, have in part joined to form a single proamniotic cavity. The mesometrial portion of this cavity is still bridged by a septum of extraembryonic ectodermal cells, closing off a relatively large space found in its mesometrial portion. With the junction of the antimesometrial and the mesometrial portions of the proamniotic cavity, the primary embryonic ectoderm and the extraembryonic ectoderm become a continuous layer, the line of union of the two portions, however, remains evident and is readily recognized in all the egg-cylinders of this tiiul oldor stap;os, a question wliicli will iccci\c fuiHu'r considoratioii in following' i)af!;(>s.


Fig. 27 Longitudinal sections ot egg-cylinders of the albino rat showing fusion of the antimesometrial and the mesomctrial portions of the proamniotic cavities. X 200. A, rat No. 81, 7 days, 22 hours; B. rat Xo. 96, 8 days; C, rat Xo. 94, 8 days, after insemination; ecl.pl., ectoplacental rone or Triiger; p.ect., parietal or transitory' ectoderm; cx.ecl., extraembryonic ectoderm; cct.ves., ectodermal vesicle, with wall composed of jirimary embryonic ectoderm, at + junction with the extraembryonic ectoderm; a.mcl.pr., antimesometrial portion of proamniotic cavity; inci.pr., mesomctrial portion of proamniotic cavity; pr.c, proamniotic cavity; r.cnl.. visceial entoderm; pr.emh.enl., primarj' embryonic entoderm.


^11 (' of n<i;in'(' 27 (rat No. 94, S da^ys) the |)roainiiio1 ic caxity foiiiis a continuous, sinf»;lo space. The fij>;ure i)resente(l is drawn fioni two s(M'ti()ns; its greater portion, to the l)ase of the ectoplacental cone from one section, the eetoplacental cone from another section. The junction of the nieinhi annus wall of the vesicle to the base of the ecto]:)lacental cone, in the two sections used for the figure, was superini|)()sed under camera lucida in joining the portions drawn from the two sections. It is heUeved that the drawing as presented gives correctly dimensions and relations of the different parts of this vesicle. The wall of the antimesometrial portion of th(> single proamniotic cavity is formed by the primary embryonic ectodci'iu, the cflls of which are for the main of irregulai' cohunnar sha|)e. with alternately i)laced nuclei. These cells are in acti\e ])roliferation, as is evidenced by numerous mitoses. The wall of the mesometrial end of the proamniotic cavity is formed of a single layer of cells of the extraembryonic ectoderm; these cells are of quite regular shape with nuclei placed in about the same plane. They stain less deeply than do the cells of the primarj^ embryonic ectoderm. In this egg-cylinder (C, fig. 27) the proamniotic cavity does not extend so near the base of the eetoplacental cone as in a number of other preparations in my possession, showing about the same stage of development; in certain of these, the .proamniotic cavity extends to near the mesometrial end of the egg-cylinder.


A more definite characterization of the different parts of the egg vesicle of the albino rat at the stage of development shown in (', figure 27, end of the 8th day, seems desirable, and in doing so I shall use the terminology used by Sobotta and Widakowich. The vesicle undei' consideration has reached a length of 0.65 nun., and a width of 0.12 mm. Somewhat more than onefourth of its length consists of eetoplacental cone or Tniger. The cavity enclosed is derived from the cavity of the blastodermic vesicle with germ disc, the blastocele, and is termed by Sobotta and AVidakowich the 'Dottersackhiihle' or yolk-sac cavity. This cavity is bounded by a thin structureless membrane derived from the parietal or transitory ectoderm and the scattered cells forming the parietal layer of entoderm. This membrane is continuous with the base of the ectoplacental cone and presents scattered flattened cells on its inner surface. I have designated this thin membrane with cells on the inner surface as the parietal or transitory ectoderm (Kolster's feinfaserige Haut). The egg-cylinder which extends to the antimesometrial end of the yolk-sac cavity, encloses the proamniotic cavity, the antimesometrial portion of which is walled by primary embryonic ectoderm, its mesometrial portion by extraembryonic ectoderm, the two forming a continuous layer, with line of union of the two types of ectoderm evident. The uncleaved extraembryonic ectoderm is continuous with the base of the ectoplacental cone. The egg-cylinder is surrounded by a single layer of cells of the visceral entoderm, differentiated so as to consist of a portion which surrounds the antimesometrial end of the egg-cylinder in relation with the primary embryonic ectoderm; the cells of this portion being of a rather thick pavement type, constituting the primary embryonic entoderm, and further a portion which covers the sides of the egg-cjdinder, with cells of a columnar type, showing special cytomorphosis. The egg-vesicles and egg-cyUnders of the stage of development under consideration and for somewhat older stages show no bilateral symmetry so far as can be discerned by study under the microscope. In longitudinal sections of egg-cylinders, cut respectively in two different planes, at right angles to each other, no difference in form, relation and structure of different parts can be observed. Selenka, Kupffer, Duval, and Sobotta have previously called attention to this fact and shown that longitudinal sections of egg-cylinders may be obtained no matter whether the sections are cut parallel to the plane of the mesometrium, thus parallel to the long axis of the uterus, or at right angles to this plane. The want of bilateral symmetry is also evident in cross sections of the egg-cylinder, as may be seen from the series of sections presented in figure 28 (rat No. 27, 7 days, 17 hours). The cross-cut egg-cylinder, from several sections of which these figures were drawn, represents a stage of develop


nicnt very similar to that of tlio ofrg-cvliiulors sliowii in longitudinal section in fif2;ure 2().

A\'i(l:ik()\vi('h, af((M- discussing- \-ei-v hi'icfly tiic mode of development of the egg-cylinder, discusses and figures an egg-cylinder of the albino rat, obtained Of days after the last coitus. His figure 3 corresponds in stage of development very closely to that shown by me in A of figure 27. In his figures, there is presented an egg-cylinder showing the anlage of the mesometrial portion of the proamniotic cavity p]mphasis is given to the fact that in the antimesometrial portion of the egg-cylinder, there may be recognized the primary embrj'onic ectoderm. His own words with reference to this point read as follows:

Der Schnitt zeigt nun sehr deutlich, dass sich die Zellen, die die antimesometrale Hohle so bcgrenzen, dass die alte Kugel-oder Eiform dieses Teiles noch zii erkennen ist — das primare eni])ryonale Ectoderm — intensiver fiirben wie die Zcllen des mesornctralcn Abschnittcs oder die des Ectoplacentarconus — das extraembryonale p]ctoderm. Die Kerne zeigen kemerlei Unterschied in der Far])ung, wohl aljer das Plasma, dass im antimesometralen Tcile von dichtcrer Structiu' zu sein schcint.


This description corresponds very closely to that given by me for a similar stage. The differentiation of these two kinds of ectoderm was also recognized hf Robinson, who states:

The epiblastic cylinder is closed at its distal end, the trophoblastic at its proximal, and the open ends of the two cylinders are in close apposition, but not indistinguishably fused, for the character of each portion of the ectoderm, after treatment with carmine, is still quite distinctive; the protoplasm of the trophol^last being tinged much more faintly than that of the epiblast.


Selenka, on the other hand, who has recognized in his 'Ektodermblase' with 'Markamnionhohle' a distinctive structure, believes this to blend completely with the Trilger. Since his account with reference to this point has influenced later workers, I may be permitted to quote him in the original. Referring to the 'Ektodermblase' with 'Markamnionhohle,' he states:

Dieser Ektodermkeim, welcher von dem vorriickenden Tragerzapfen anfanglich sehr wohl abgegrenzt ist, indem beiderlei Gebilde sich in Folge der convexen Kriimmung ihrer einander zugekehrten Flachen sozusagen nur in einem Punkte beriihren, fliesst endlich mit dem Trager vollstandig zusammen, und zwar bei der Waldmaus bevor, bei der Ratte und Hausmaus aber nachdem die Markamnionhohle enstanden war.

Fig. 28 A series of cross sections at different levels of an egg-cylinder of the albino rat after the anlage of the antimesometrial portion of the proamniotic cavity. X 200. Kat No. 27, 7 days, 17 hours, after insemination. The sections selected for the several levels drawn, A to D, are as follows: A, middle of ectoplacental cone; B and C, through extraembryonic ectodermal portion of egg-cylinder, just below junction with ectoplacental cone (B), and just above ectodermal vesicle (C); D, through middle of ectodermal vesicle. Compare with B, figure 26, a longitudinal section of an egg-cylinder of the same stage of development; p.ect., parietal or transitory ectoderm; ex.ect., extraembryonic ectoderm; pr.emb.ect., primary embryonic ectoderm of the ectodermal vesicle; v.ent., visceral entoderm; pr.e.mh.ent., primary embryonic entoderm; a.met.pr., antimesometrial portion of jiroamniotic cavity.


That the proamniotic cavit}' of the egg-cylinder of the albino rat has its anlage in two distinct cavities, the one developing in the ectodermal node in the antimesometrial portion of the eggcylinder, which is the first to develop; the other in the mesometrial portion in the extraembryonic ectoderm, was recognized by Selenka (fig. 30, plate 14, E, ^Markamnionhohle, E', falsche Amnionhohle) , Duval (fig. 100,) Robinson, and Widakowich (fig. 3). Corresponding stages of egg-cylinder development as presented by me in figures 26 and 27, for the albino rat, are shown by Sobotta ('02), for the mouse in his figures 12 to 14 and text figures a to f. On comparison of my figures with Sobotta's, it becomes evident that the egg-cjdinder of the rat is much longer and more slender than that of the mouse. According to the account of Sobotta, the egg-cylinder of the mouse, soon after its anlage, shows by reason of a distinct transverse furrow^ a division into tw^o parts, an antimesometrial portion of globular form, surrounded by a visceral layer of entoderm, corresponding to w^hat I have designated as the ectodermal node; and a mesometrial portion w^hich early. shows the anlage of a proamniotic


(•:i\it y. A luiiicii is ohtniiicd in the :iiit iiiicsoiiict ii;il poi't ion. latcitlian ill the iiicsonict ii;il poi'tioii. As devel()|)iiiciit pi'ofoeds, this sharp tlcinarkalioii of antiniesometrial and iiicsoinotrial portion is graduall}' lost. This, as stated in his own words, reads:

Sehcn wir von dom tlic (dor Kcimhrihh' zii{!;('kcliilc) ObcrHiicho des Cylinders iiborzichcndtMi Dottciontodcnii zuiiadist ah, so sicht man, dass die Furche, welchc die oben erwahntcn inesonietralen und antiniesonietralen Abschnittc in Stadiuni der V\^. 11 u. 12 trcnnte, jetzt wiedcr wcnig deutlicli ist. Ks bahnt sich cine Verschnielzung beider Abschnittc wi(Mleruni an, was man am leicliteston daraus ersieht, dass bald (Fig. 14) beide Abschnitte ein gemeinsames Lumen erhalten.


With the formation of a continuous proamniotic cavity, this is bordered by a single layer of 'ectodermal cells,' with alternately placed nuclei. The cells are described as being the same throughout; neither in text nor figure does Sobotta differentiate between ectodermal cells derived from the antimesometrial portion of the egg-c^dinder and those derived from the mesometrial portion. Melissinos also recognizes antimesometrial and mesometrial portions in the development of the eggcylinder of the mouse, in his figure 34. According to this observer, the antimesometrial portion of the proamniotic cavity is the first to appear; later it appears in the mesometrial portion, the two cavities joining as development proceeds. The parts of the ectoder?n derivetl from these two poi'tions may be recognized, however, after a single proamniotic cavity has developed. This Melissinos states in the following words: "Trotz aller Vereinigung der beiden Hohlungen bleibt die Unterscheidung des normals abgesonderten antimesomtralen Abschnittes von dem mesometralen immer leicht zu machen, sei es durch eine klare Grenzlinie oder durch eine an der Peripherie des visceralen Dotterblattes befindhche Furche." The account of ^Melissinos is more in agreement with the presentations as observed in the albino rat than is that of Sobotta.


Selenka, Sobotta, and [Melissinos recognize three different regions of constriction to which significance is given, in the egg-cylinder of the mouse. As stated by Sobotta, the first constriction is in the region of the original furrow which demarks the antimesometrial and the mesometrial portions of the eggcylinder, the region of the primary amniotic fold; the second where the mesometrial cavity ends; and the third where the original blastodermic cavity reaches its mesometrial end. The three folds recognized by Melissinos, are characterized by the specificity of the ectoderm. Since his statement concerning this point is somewhat involved, I find it necessary to use his own words; they read as follows, referring to these folds he states:

Der eine derselben a liegt antimesometral und ist der bekannte erste kugelformige Buckel (Ektoderm) mit den langlichen, cylinderpyramidalen oder polygonal-pyramidalen Zellen; der zweite h liegt in der Mitte und besteht aus kubisch-polygonalen Zellen, und der dritte Buckel c, aus polygonalen Zellen bestehend, liegt mesometral und ist von dem mittleren durch Einschnlirung, von der Basis des Ectoplacentarconus aber durch die bekannte Urfurche des Eicylinders getrennt, in der sich das viscerale Dotterblatt zuni parietalen Dotterblatt umbiegt.


So far as I am able to determine, the account of jMelissinos agrees with that given by Sobotta, as concerns the folds of the egg-cylinder of the mouse. Selenka's account need not receive special consideration.


In well-fixed egg-cylinders of the albino rat no such folds are recognized. At the line of junction of the primary embryonic ectoderm and the extraembryonic ectoderm, a slight infolding of the layers, variable in degree, is recognized. Other foldings of the wall of the egg-cylinder I have regarded as accidental and not of special significance. Therefore, I am wholly in accord with Widakowich, who has also discussed this cpiestion with reference to the albino rat and has described the low fold in the region of the junction of the primary embryonic ectoderm and extraembryonic ectoderm. Referring to that fold, he states: "Dass war die einzige konstante, bald starker, bald schwiicher ausgepriigte Einschnlirung der Proamnionhohle."


Sobotta deserves credit for having described fully the differentiation and cytomorphosis of the cells of the visceral entoderm of the egg-cylinder, and since his observations on this point apply in the main to the albino rat, they may at this time be given consideration. Dining tlic early stages of cfr^-cyliiuler dii'ferentiation and aiilage of the proanmiolic caxity, the layer of visceral entoderm diH'erontiatcs into a ])ortion whieh is in relation with the primary embryonic ectoderm of the antimesometrial portion of the egg-cylinder, in which region the cells of the entoderm are first of short cubic shape, later of the pavement type; this portion may be regarded as forming the primary embryonic entodei'm, since it forms the greater part of the entoderm of the embryo. The greater part of the visceral entoderm, that which surrounds the sides of the mesometrial portions of the egg-cylinder, consisting of extraembrj'onic ectoderm, differentiates into cells of the columnar type. In this latter portion, with the formation of a continuous proamniotic cavity, the entodermal cells undergo characteristic cytomorj)hosis. In them, as stated b}' So})otta, there may be recognized three main zones: (1) a basal zone with denser protoplasm containing the nucleus; (2) a middle zone with markedly vacuolated protoplasm; (3) an outer zone in which hemoglobin granules are recognized, the latter zone staining deeply in eosin. These three zones in the cells of the visceral entoderm in the region of the extraembryonic ectoderm of the egg-cylinder may be recognized in figures 20 and 27, not so clearly as in Sobotta's colored figures, particularly his figure 17 ('03) and figure 8 ('11). However, I am able to follow closely his description in my own preparations of a somewhat older stage than thus far ligured. It is Sobotta's contention that in the extravasated blood surrounding the egg vesicle, in close apposition to its thin outer wall, there may be observed many red blood cells which, though presenting normal form, show a distinctly granular content. These granules stain deeply in eosin and are in shape, size, and reaction to stain very similar to granules found in the peripheral part of the cells of the visceral entoderm. On the outer surface of the thin wall of the vesicle; on its inner surface; in the cells lining this; in the yolk sac cavity; and on the outer surface of the cells of the visceral entoderm, similar granules are found. These appearances are interpreted as showing an absorption of maternal hemoglobin by the entodermal cells of the mesometrial portion of the egg-cylinder.


Sobotta's statement concerning this point, which, owing to its importance, I quote in full, reads as follows:

Man wird diese mikroskopisch erkennbaren Verhaltnisse nicht anders deuten konnen als in folgender Weise: Die Hamoglobinschollen,

die durch die aussere Wand des Dottersackes in die Dottersackhohle gelangt sind, werden von der Oberflache des zylindrischen, die ganze Seitenflache des Eizylinders liberziehenden visceralen Dottersaclvepithels aus resorbiert und zwar geschieht das in der Weise, dass die Hainoglol)inschollen ziinachst als solche in der Zelle selbst eintreten, dann aber ini vacuolisierteii Tell der Zelle gleichsam verdant werden, wobei die einzelnen kleinen Schollen vorher zu grosseren Tropfen zusammen-fliessen scheinen.


My own observations on the albino rat as concerns this phenomenon, more particularly as concerns the structure of the cells of the visceral entoderm in the region of the extraembryonic ectoderm, corroborate Sobotta in many particulars. This question will be again and more fully considered in a contemplated later publication dealing with the implantation and decidua formation in the albino rat. It could not be considered now without a discussion of the changes involved in the development of the decidua, a question which I am not prepared to consider fully now. It may be stated, however, that judging from my own preparations and the figures of Grosser, the extravasation of blood into the egg chamber is not nearly so extensive in the albino rat as is shown in the figures of Sobotta for the mouse.


The thin membrane which surrounds the yolk-sac cavity, which I have designated as the parietal or transitory ectoderm, is derived in development from the parietal or transitory ectoderm, and the relatively few parietal entodermal cells, as described and figured for younger stages. At the stage of egg-cylinder development under consideration — with continuous proamniotic cavity — this structure appears as a thin, practically homogeneous membrane with scattered, flattened nucleated cells on its inner surface. Sobotta regards these cells as derived from the parietal entoderm, the cells of the parietal ectoderm having disappeared. As concerns this, I am unable to speak with certainty, since the Congo red solution used as a double stain is not particularly favorable in differentially coloring these cells. However, I am disposed to regard these flattened cells as deriv(Ml from Ihc i);uietal ectoderm. The parietal entodermal cells arc never numerous in the rat, and mitotic figures are seldom observed in them. With the extension of the vesicle with the enlargement of the blastocele, the cells of the parietal or transitory ectoderm become attenuated until they appear for the greater part as a thin cuticular membrane, and I am disposed to regard the flattened nucleated masses of proto])lasm lining the inner surface of this membrane as derived from the cells of the parietal ectoderm.


Much attention has been given to certain large cells which are found in close relation with the outer surface of this thin membrane. These cells, generally referred to as giant cells (Riesenzellen) were, by Duval, Sobotta (earlier publicjitions) and Grosser thought to be of embryonic origin and dcri\'ed from the cells of the parietal ectoderm. Selenka, Disse, Kolster, Melissinos, Pujiula, Widakowich, and later Sobotta ('11) regard them as derived from the maternal tissue and as representing differentiated decidual cells. It is not mj^ purpose to consider more fully these cells in the present communication, since they are by me not regarded as of embryonic origin, ^ly own observations as concerns them agree in the main with those of Widakowich, who, in the albino rat has followed their origin from decidual cells. Since not of embryonic origin, they have been disregarded in making the figures.


I have previously, in connection with a discussion of the structure of vesicle C, figure 24, alluded to the fact that the cells of the ectoplacental cone as also the cells of the parietal or transitory ectoderm have a phagocytic action for maternal blood cells. This Sobotta has also observed for the mouse, in which he is confirmed by Kolster who has further shown that the cells of the ectoplacental cone also take up fat particles. With the ingestion of maternal blood cells by the cells of the ecto})lacental cone, more particularly, with the absorption of hemoglobin by the entodermal cells of the mesometrial portion of the eggcylinder, a period of rapid growth of the egg vesicle is initiated. To this Sobotta has called attention for the mouse; the same is evident in the albino rat. Indeed, Sobotta presents the far-reaching conclusion that the explanation of the phenomenon of germ layer inversion or entypy of the germ layers is to be found in the dearth of food supply of the ovum in the stages preceding the formation of more definite relations between the ova or germ vesicles with the decidua. It is thought by this observer that the inversion of the germ disc has for its purpose the increase of the absorptive surface of the visceral or yolk sac entodermal epithelium, which as a differentiated layer comes to surround nearly the whole of the egg-cylinder on completion of the inversion, and is thus increased in extent and brought in relatively close relation with the maternal blood lacunae surrounding the egg vesicle.



Normal: Introduction | Materials and Methods | Ovulation, Maturation and Fertilization | Pronuclear Stage | Segmentation Stages | 2-ceIl stage | 4-ceIl stage | 12 to 16-ceIl stages | Summary of segmentation stages | Completion of segmentation and blastodermic vesicle formation | Blastodermic vesicle | Late stages blastodermic vesicle | Egg-cylinder formation | Late stages in egg-cylinder | Conclusions | Literature cited | Figures
Abnormal: Introduction | Half Embryos in Mammalia | Degeneration of ova at the end of segmentation | Incomplete or retarded segmentation | Abnormal segmentation cavity formation | Degeneration of ova as a result of pathologic mucosa | Imperfect development of ectodermal vesicle | Two egg-cylinders in one decidual crypt | Conclusions | Literature cited
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Cite this page: Hill, M.A. 2017 Embryology Book - The Development of the Albino Rat 8. Retrieved December 18, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_The_Development_of_the_Albino_Rat_8

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