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| {{Ref-Holyoke1936}}
| | #REDIRECT [[Paper - The role of the primitive mesothelium in the development of the mammalian spleen (1936)]] |
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| Edvvard Agustus Holyoke
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| Department of Anatomy, College of Medicine, University of Nebraska, Omaha,
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| Nebraska
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| TWO PLATES (rwrmvn mavens)
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| It is generally accepted that the embryonic mammalian
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| spleen can first be recognized as a dense accumulation of cells
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| in the mesenchyme of the dorsal mesogastrium or neighboring
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| rnesentery; The splenie rudiment has been described by
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| Kolliker (1854), Miiller (1870), Minot (1892), Kollmann (’O0),
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| Tonkoff (’0O), Sabin (’12), Thiel and Downey (’21) and many
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| others. Choronsehitzky (’OO) and Danchakoff (’16) have observed a similar anlage in birds. Radford ( ’-08) believed the
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| splenic anlage’ of the frog to be a dense accumulation of
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| lymphocytic cells around the mesenteric artery, While Leon
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| (’32) placed it (in fish) at a definitely predetermined point in
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| the vascular endothelium of the sub—intestinaI vein.
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| The old controversy concerning the germ layers involved in
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| the developing spleen has apparently been settled, the
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| generally accepted view today being that it is entirely of ‘mesodermal origin. However there still exists some doubt as to
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| which mesodermal elements are directly involved. In a recent paper, Bergel and Gut (’34) have ‘attempted to establish
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| the human spleen as a derivative of mesenchyme alone as has i
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| been held for birds and reptiles by Danchakoff (’16) and
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| others, and for Amphibia by Nakajima (’29). On the other
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| hand Kollmann (’OO), Tonkofi (’00), Choronschitzky (’00),
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| Thiel and Downey (’21) and I-Iartmann (’30) have shown that
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| the spleniclrudiment receives cells from the overlying peri
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| toneal layers which are crowded into the mesenchyme during the early stages of development. Toldt (1889), and Janosik
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| ( ’01) were of the opinion that the spleen was exclusively mesothelial in origin.
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| Recently I have had occasion to examine the splenic region
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| of an extensive series of early human‘ and pig embryos sectioned in various planes and stained by several different
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| methods. Observations of this material have led me to conclusions differing from those of Bergel and Gut.
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| Inasmuch as most descriptions of the mesenteries before
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| the splenic rudiment appears have been very incomplete, a
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| careful examination of very early material was made. As
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| an exception to such incomplete descriptions stands the work
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| of Thiel and Downey (’21) ; these authors described the dorsal
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| mesogastrium of a 3—mm. gopher embryo, in which stage they
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| found a definite mesentery covered by a loose visceral peritoneum and containing a few formed capillaries. These
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| authors have also described the dorsal mesogastrium of the
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| pig embryo (7.5 mm.) before the appearance of the spleen.
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| In human embryos of 3 mm? I have found no indication
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| whatever of the future splenic rudiment. The region in which
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| the rudiment is to appear can, however, be roughly determined
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| by its relation to the stomach. Examination of the mesentery
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| in that region reveals no characteristic findings. Like all
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| other parts of the mesentery it consists of a comparatively
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| loose mass of mesenchyme covered on its lateral surfaces by
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| dense mantles of irregularly arranged cells which are three or
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| four layers deep. This coelomic epithelium or primitive mesothelium is in a state of active proliferation as evidenced by
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| many mitotic figures. The cells composing these layers bear
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| a striking resemblance to those of the underlying mesenchyme
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| ’ Of the human embryos examined some were from the collection of the Depart~
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| ment of Histology and Embryology, Cornell University Medical College, Ithaca;
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| some from the collection of the Department of Anatomy, Harvard Medical School;
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| and the remainder from the collection of the Department of Anatomy, University
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| of Nebraska Medical College. The author is most appreciative of the generosity
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| of Dr. B. F. Kingsbury and Dr. J. L. Bremer, who permitted the examination of
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| this material and the use of some of the figures herewith reproduced. Pig
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| embryos examined were locally collected and prepared by the author.
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| “All measurements of embryos given in this paper refer to crown-rump length.
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| in that they take an identical cytoplasmic stain and their nuclei
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| are large, containing a few dense masses of chromatin and
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| usually two nucleoli. They are intimately connected with the
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| mesenchyme, protoplasmic continuity being demonstrable in
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| many places. The possibility of .many cells passing from coelomic epithelium to mesenchyme can be readily shown by the
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| intimate contact and irregular boundary between the surface
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| layers and underlying tissue, and by the presence of mitotic
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| spindles lying perpendicular to the surface of the mesentery
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| as described by Thiel and Downey for the 7 .5—mm. pig embryo.
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| Essentially the same conditions have been observed in other
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| human embryos up to 6 mm. in length. By the time this stage
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| has been reached, the stomach has become a large conspicuous
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| organ and has started its rotation toward the left. In -rotating
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| it has carried a fold of the mesogastrium with it so that, as
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| seen in transverse section, it makes one acute bend at its root
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| where it joins the body wall and another at its stomach attachment (fig. 1). Near the midpoint of this mesenteric segment there has developed a distinct bulging toward the left.
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| This bulging of the mesentery is due to a proliferation of
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| mesenchymal cells in that region, but there is no demonstrable
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| condensation. The coelomic epithelium there has retained all
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| of the characteristics described for the earlier embryos. It
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| has remained an irregularly formed mantle of cells continuous
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| With the underlying mesenchyme, and as indicated in the
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| earlier forms, presenting no cytological characteristics which
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| would enable one to distinguish between the two. The only
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| variation of any kind is a slightly deeper’ cytoplasmic stain
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| in the surface cells due, possibly, to crowding.‘
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| Elsewhere the general coelomic epithelium has started to
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| differentiate. In most regions it has become a cuboidal or
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| squamous layer sharply cut off from the mesenchyme by a
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| distinct basement. membrane. Examples of this are to be
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| seen in figure 1. It will be noted that the coelomic epithelium
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| on the right side of the mesogastrium has become cuboidal,
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| but that the basement membrane is not yet demonstrable.
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| There remain, however, a few other areas where the coelomic epithelium has retained its earlier form, notably in a series of
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| irregularly located points along the gut. These same conditions are to be found in pig embryos of 7.5 to 8 mm.
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| The above described bulging of the mesentery probably
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| should not be considered as the splenic anlage for a definite,
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| much less extensive condensation of cells soon appears in this
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| region. In 10- to 12-mm. pig embryos this mass is present
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| in the left part of the mesentery Where it is continuous with
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| both the primitive mesothelium and the mesenchyme (fig. 2).
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| It does not stand out very conspicuously at this stage because
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| of the density of the mesenchyme in general. The cellular
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| mass is not in contact with the mesothelium of the right leaf
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| of the mesentery, but is separated from it by a small area of
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| looser mesenchyme.
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| A closer study of the region of the anlage in the 10—mm. pig
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| embryo (fig. 2) fails to reveal any line of demarcation between
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| mesothelium and dense mesenchyme. As indicated in the
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| earlier stages of pig and human embryos continuity between
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| the two can be demonstrated and no cytological differences,
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| except as noted, are to be found to separate them. Mitoses
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| are abundant and these occur alike in the deeper cells of the
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| anlage and the free surface of the mesentery A few of the
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| latter figures still present spindles perpendicular to the surface indicating a contribution of cells from this region to the
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| deeper mass. All of these cells have a very similar morphology. The deeper mesenchymal cells are so densely
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| packed that their intercellular bridges are difficult or impossible to distinguish as separate cytoplasmic strands, and
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| their typical stellate form is obscured. These cells, as Well as
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| those near the surface, take a deep basic cytoplasmic stain
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| against which the vesicular nuclei stand out as comparatively
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| pale bodies.. The nuclei are still characterized by a few dense
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| chromatin masses and two nucleoli, as in the earlier embryos.
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| The less dense mesenchyme at the right of the anlage shows
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| nuclei identical to those just described. The cytoplasm of
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| these cells stains less deeply and the typical stellate form is
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| more readily demonstrable. Similar conditions obtain in
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| human embryos of from 8 to 9 mm. in length.
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| From these findings one is forced to two conclusions. First,
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| there is no morphological basis for believing that the primitive
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| mesothelium is more than a. dense layer of littoral mesenchymal cells which later differentiate to form tl1e adult peritoneal epithelium. Second, both the surface and deeper layers
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| play an important role in the contribution of cells to the
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| splenic mass.
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| It has been repeatedly shown that primitive mesothelial cells
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| are pleuropotential and that invasion of the deeper tissues by
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| them is of frequent occurrence (Schott, ’O9; Mollier, ’O9;
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| Bremer, ’14; Ilaff, ’14; Scammon, ’15; and others). Emmel
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| (’16) thought that many of the free cellular elements found in
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| the peritoneal cavityof the pig embryo were derived from
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| this same source.
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| The time of appearance of a definite splenic anlage seems
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| to be relatively constant in many mammalian species. I have
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| found it in human embryos at 7.5 to 8 mm. Tonkoff (’00),
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| Kollmann ( ’OO), Sabin (’12), Ono (’30) and others have described the splenic rudiment in embryos of from 8 to 10 mm.
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| or during the fifth week of development, while Bergel and Gut
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| (’34) found it at 7 mm. In the pig embryo the time of appearance of the spleen may be a little more variable. In some of
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| the series of embryos I have examined, it was poorly developed at 12 mm., while some 10—mm. series showed it distinctly. It is possible that slight errors in measurement and
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| failure to make adequate allowance for shrinkage during
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| preparation may account for this variation. Thiel and
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| Downey (’21) described a definite splenic anlage in the pig
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| embryo at 15 mm., and a well-developed splenic rudiment in
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| the striped gopher at 8 mm. In an 8-mm. cat embryo which I
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| examined, it could be identified clearly.
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| After the splenie mass has been established, it grows very
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| rapidly causing a more and more marked local bulging of the
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| mesentery which gradually replaces the more diffuse enlargement of the earlier presplenic stages. At the same time the
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| mesentery begins to buckle toward the left at the splenic
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| prominence so that this structure soon lies in the convexity of a definite fold (figs. 4, 5, 7 and 9). Coincidentally, the
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| coelomic epithelium begins to become separated from the
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| splenic anlage as a distinct layer. This is first indicated by
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| the organization of the cells into a single layer and the appearance of a distinct basal zone, free from nuclei and conspicuous
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| because of its light color. Ono (’30) has mentioned this zone
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| in the early human embryo. In my opinion this light zone
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| owes its appearanc solely to segregation of the nuclei in more
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| peripheral portions of the superficial cells. This leads me to
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| the conclusion that the plane of sectioning is not oblique
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| enough in relation to the epithelial surface seriously to distort
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| the picture. These changes just noted are usually demonstrable in 12-mm. pig embryos (fig. 3), although at many
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| points the cellular arrangement is still irregular. and protoplasmic continuity with the mesenchyme is evident. At a, b,
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| and c are shown small groups of cells continuous with the
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| coelomic epithelium, interrupting the light zone and apparently making their way into the splenic mesenchyme. In a
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| few places in this surface layer there are signs of nuclear
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| differentiation, the chromatin breaking up into finer particles
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| than in the mesenchymal nuclei. Ad basement membrane soon
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| appears in several places and begins to extend along the deep
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| surface of the light zone. Between the Various segments of
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| this membrane, protoplasmic continuity with the mesenchyme
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| remains and the migration of superficial cells apparently continues. The organization _of epithelial cells is complete in
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| human embryos of from 10 to 12 mm. (fig. 4). These cells
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| become more distinctly separated from each other by cell membranes a11d the general nuclear stain becomes more intense. In pig embryos of 14 to 15 mm. a similar series of
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| changes begins. In a 14-mm. pig embryo the organization of
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| the epithelium into a distinct layer’ is almost complete and the
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| light zone is conspicuous. The basement membrane has not
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| appeared except in a few isolated places and cells are still
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| passing into the underlying mesenchyme (fig. 8).
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| Soon after the organization and dfferentiation of the
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| coelomic epithelium has begun the basement membrane is almost complete, cutting off a distinct layer of columnar cells.
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| When the basement membrane appears, it is readily demonstrable by ordinary staining methods. In a typical human
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| embryo of 13.5 mm. the membrane stands out conspicuously
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| as a sharp line broken only in a few places by migrating cells
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| (fig. 5). One of these regions is shown in more detail in
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| figure 6. The continuity of the coelomic epithelium with the
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| splenic mesenchyme has remained unbroken at this point, and
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| a cell (mc.) is being added to the splenic anlage. There
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| probably is only an occasional cell added to the mesenchyme in
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| this manner subsequently, for (as can be seen in figs. 5 and 6) the mesothelium is now a distinct layer and is sharply demarcated in most places. A closely graded series of nuclei can
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| now be found in this mesothelial layer; representing various
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| steps between the primitive mesothelium, which is identical
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| with the mesenchyme, and the general mesothelium of this
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| stage of development. A few of these nuclei retain mesenchymal characteristics (fig. 6): Others show a finer distribution of chromatin and the disappearance of one or both
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| nucleoli; and still others are intensely stained and contain
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| finely divided chromatin, in some cases appearing as a
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| delicate network. These are typical of the general mesothelium. There has also been a progressive limitation of the
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| more primitive type of mesothelium to the splenic region
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| alone. In early human embryos (figs. 1 and 4) this primitive
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| non-specific layer extends beyond the locus of the splenic
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| anlage over the surface of the stomach. Going beyond this
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| region in 6- to 7-mm. human embryos, one sees a gradual and
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| continuous transition to the general coelomic epithelium
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| (fig. 1). Later (fig. 5) this transition begins definitely at the
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| margin of the spleen. The cells become progressively more
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| and more flattened as the layer is traced away from the spleen,
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| the light zone narrower and the nuclear stain more intense.
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| The general coelornic epithelium is a low cuboidal or squamous
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| layer and somewhat resembles the adult condition.
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| During the same period the splenic mass becomes more distinct from the surrounding mesentery, the transition from dense to loose mesenchyme becoming more abrupt and the
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| mesenchyme of the mesentery more attenuated. At 11 mm.
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| (fig. 4), the human spleen is not Very clearly marked off, but
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| at 13.5 mm. (fig. 5) the limits of the anlage are very distinct.
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| Similar changes have appeared in the splenic anlage of the
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| 14-mm. pig embryo (fig. 7). The dense mesenchyme here is
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| beginning to show sharp localization. It can be distinctly
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| differentiated from the loose mesenchyme to the right but is
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| not so definitely demarcated on all sides, tending to merge
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| more gradually into the looser surrounding tissue.
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| As the spleen continues to grow, it expands in the left half of
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| the mesentery and grows around the loose mesenchyme at
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| the right (fig. 9). The large splenic vessels are found here in
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| the concavity of the splenic fold (figs. 4, 5 and 7) and this
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| region becomes established as the hilus. This arrangement is
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| definitely shown by human embryos of from 15 to 16 mm.
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| From this time on the coelomic epithelium over the spleen
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| diflerentiates rapidly. The light zone becomes narrower as
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| the cells begin to assume a low columnar or cuboidal form, and
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| the basement membrane becomes complete (fig. 9). There remain a few irregularities, in the deep surface of the mesothelium, but it is doubtful whether they could be interpreted
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| as indicating it further exchange of cells. This process is
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| probably complete in human embryos of 14 mm. and in pig
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| embryos of from 15 to 19 mm. The coelomic epithelium of a
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| 22-mm. pig embryo is composed of cells regularly placed upon
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| a definite basement membrane which are sharply separated
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| from one another by distinct cell membranes. By this time
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| they difier from the general mesothelium only in that they are
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| cuboidal rather than squamous in form. This latter condition
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| is not attained in the splenic region of pig embryos before they
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| reach a length of 45 to 50 mm. Figure 11 shows a cuboidal
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| layer over the spleen at 35 mm. In man the adult type of mesothelium appears at a much earlier stage. The mesothelial layer over the spleen at 22 mm. is identical in every way with.
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| the general coelomic epithelium and is approaching the adult
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| condition.
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| Bergel and Grut (’34) have recently denied any contribution
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| by the eoelomic epithelium to the underlying mesenchymal
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| anlage of the mammalian spleen. Nakajima (’29) ha.s come
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| to similar conclusions in a study of amphibian embryos.
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| From Nakajima’s discussion and figures, I am unable to determine how these conclusions were reached. Bergel and Gut
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| (’34) made an extensive study of human material. In their
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| opinion most investigators have been misled on the mesothelial question, because they have failed to use specific stains,
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| and have studied sections which have not cut the epithelial
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| layers transversely. They state that the basement membrane
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| between the coelomic epithelium and the underlying mesenchyme is demonstrated only by strong cytoplasmic stains, and
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| that the usual technical methods fail to show it. With this
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| statement in mind, I have reexamined all of my material,
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| some of which has been stained with M-al1ory’s connective
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| tissue stain and some by B.ielschowsky’s silver impregnation
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| method. I can find no instance in which these preparations
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| show a complete basement membrane between the eoelomic
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| epithelium and the splenic anlage in pig embryos of less than
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| 15 mm. On the other hand very distinct basement membranes
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| are demonstrable in relation to the general eoelomic epithelium
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| in preparations stained with Delafield’s hematoxylin and
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| azure II eosin, or with Wright’s and Giemsa stains. All of
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| the material used for illustrations of this paper (except fig. 9,
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| where orange G was used with hematoxylin) has been stained
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| by these or similar methods. Basement membranes are conspicuously demonstrated at some point in most of these figures.
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| Figure 1, page 24 of Bergel and Gut ’s paper, they considered
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| a demonstration of a complete basement membrane in the
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| splenic region of an early human embryo (14 mm.). In my
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| opinion this membrane is no more distinct than that shown by
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| other methods in my material. Furthermore the leader
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| pointing out the membrane in their figure could be interpreted as indicating a typical break with the continuity between
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| superficial and underlying cells.
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| In regard to the plane of sectioning of the material, there
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| is no doubt that misleading impressions can be given by
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| sections which are not truly transverse through the layers in
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| question. However, the condition of the coclomic epithelium
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| here represented (except where specially noted) is not to be
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| explained on this basis. Regardless of the plane of sectioning,
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| the condition of the mesothelium over the splenic region (figs.
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| 1 to 9) is a constant finding in these early embryos. On the
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| hilar side of the dorsal mesogastrium in the same sections,
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| the mesothelium is a cuboidal or squamous layer. Further
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| evidence that these sections are nearly transverse was ob
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| tained by tracing the layer through several sections and ,
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| demonstrating that it shifts only slightly in relation to other
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| structures, surely no more than the comparatively fiat layer
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| on the opposite side of the mesentery. In those stages where
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| several layers of primitive mesothelial cells are found, care
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| was taken to demonstrate that similar conditions were not
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| present on the opposing surface. Also, there are other findings such as cytoplasmic continuity between layers, the
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| presence of transitional cell types and mitotic spindles perpendicular to the surface of the mesentery, which are not to be
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| explained on the basis of plane of section.
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| Bergel and Gut agree with Hartmann ( ’30) that cords of
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| epithelial cells can be seen growing down into the rudiment.
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| They maintain, however, that these cells are surrounded by a
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| definite basement membrane andlare not incorporated in the
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| mesenchyme. In their figures. one could not definitely determine such a membrane.
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| Finally these two authors state that, because two types of
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| cells are not demonstrable in the splenie anlage, this structure could have been derived from one source only. While it
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| is true that Toldt (1889), Janosik (’01) and others have
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| thought that the free cellular elements of the mammalian
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| spleen were cut off from the coclomic epithelium and entered
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| _a mesenehymal meshwork, and more recently Radford ( ’O8),
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| Leon (’32), and others have found free cellular elements at
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| early stages in lower forms, Thiel and Downey (’21), Danehakoff (’16) and others have shown than in anmiotes the
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| splenic rudiment contains no free cells until a later time, and
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| that such cells are cut off from the mesenchymal syncytium
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| when they do form. This is in accord with my own observations. I am aware of no contention made by recent authors
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| that the coelomic epithelium contributes free elements or any
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| differentiated forms whatever to the spleen. The evidence
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| rather points toward the continuity of mesothelium and mesenchyme. The cells which are crowded into the latter layer are
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| originally a part of the syncytium and remain so. 'In conclusion I should like to point out that the contribution
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| of cells from the coelomic epithelium is important more because it indicates that this layer is essentially mesenchymal
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| in its nature and potentialities than because it indicates a
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| dual source of the splenic rudiment. As the coelomic epithelium is becoming a differentiated layer, this contribution continues sparingly for a time; but. after a certain critical
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| point is reached, it ceases entirely.
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| SUMMARY
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| The splenic rudiment appears in the human embryo at 7.5
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| mm. and in the pig embryo at 10 mm. It is first observed in
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| other mammalian forms at comparable stages.
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| The anlage develops as a dense mass of mesenchyme in a
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| preformed bulging of the dorsal mesogastrium. It is at first
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| continuous with the overlying coelomic epithelium and the
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| mesenchyme of the mesentery. It gradually becomes more
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| sharply delineated from this latter tissue, which becomes more
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| diffuse as the anlage becomes more condensed.
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| A small area of loose mesenchyme always separates the
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| anlage from the right leaf of the mesentery. The splenic
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| vessels appear in this area and the spleen grows around it
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| forming the hilus at this point.
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| Before the splenic rudiment appears the coelomic epithelium
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| is present as a surface condensation of mesenchyme continuous with the underlying tissue.
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| The spleen forms at the base of the littoral condensation to
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| the left of the dorsal mesogastrium and is derived in part
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| from this and in part from the underlying mesenchyme. The
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| surface layer over the spleen retains its primitive character
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| for a much longer period than coelomic epithelium in general.
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| Differentiation of the primitive coelomic epithelium in contact With the splenic rudiment can first be recognized by an
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| organization of the component cells into a simple cuboidal
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| layer. This layer later becomes sharply cut off from the
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| underlying tissue by a definite basement membrane. Until
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| this membrane becomes complete some of the cells retain their
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| primitive potentialities as is evidenced by their mesenchymal
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| type of nucleus and by their occasional migration into the
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| splenic mesenchyme.
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| After the basement membrane becomes complete, all migration ceases. These mesothclial cells then become progressively
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| flattened until the adult squamous form is approached. This
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| condition is attained at a much earlier stage in the human
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| embryo than in the pig.
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| The primitive mesothelium plays an important role inthe
| |
| development of the mammalian spleen. This role indicates
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| mesenchymal potentialities in the primitive mesothelium
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| rather than a dual source of the spleen.
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| LITERATURE CITED
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| BERGEL, A. AND H. GUT 1934 Zur Friihentwicklung der Milz beim Menschen.
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| Zeitschr. f. Anat. u. Entwicklungsgesch, Bd. 103, S. 20-29.
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| BREMER, J. L. 1914 The earliest blood vessels of man. Am. J. Anat, vol. 16, pp.
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| 447475.
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| CHORONSCHITZKY, B. 1900 Die Entstehung der Milz, Leber, Gallenblase, u. s. w.
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| bei den verschiedenen Abteilungen der Wirbeltiere. Anat. Hefte, Bd.
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| 13, S. 369-614.
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| DANCHAKOFF, V. 1916 fiber die Entwieklung des Blutes in den Blutbildungsorganen bei Tropidonotus Natrix. Arch. f. mikr. Anat., Bd. 87, S.
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| 497-584.
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| | |
| —————~———— 1916 The equivalence of difierent hematopoietie anlages by method
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| of stimulation of the different stem cells. Am. J. Anat., vol. 20, pp.
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| 255-327.
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| | |
| EMMEL, V. E. 1916 Concerning certain cellular elements in the coelomic
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| cavities and mesenchyma of the mammalian embryo. Am. J. Anat., vol. ‘
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| 20, pp. 73-123.
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| MESO'l.‘1LE.LIT7M IN 1'r.u: I)EVELOI’M.EI\TT 05' s1>L1sm: 345
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| | |
| HAI011‘, It. 1914 Bindgewebes und Blutbildungsprozesse in der en1bryo11a1en Leber
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| des I-Iulms. Arch. 1''. mikr. Anat., Bd. 84, S. 321-350.
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| HARTMANN, A. 1930 Die Milz. Ilandbueh den Mikroskopisehen Anatomie des
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| Mensohen. W. V. Mb'1Ie11dor1'.'e. Bd. 6, S. 397-563. Julius Spxingex-_
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| Berlin.
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| | |
| JA‘.\Io§IK, J} 1901. Bemerkungen zur der Arbeit Dr. W. Tonkoff, Die Entwicklung
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| den Milz bei den Anmioten. Arch. f. Inikr. A11at., Bd. 57, S. 487-488.
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| | |
| ]<{i1.LIKER, A. 1854 Manual of Hum:-m Ilistolegy, vol. 2, pp. 138— L60. Transl.
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| by Brusk and Huxley. Sydenham Society, London.
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| | |
| KOLL1\IA.\'I\', J. 190() Die Entwieklung der Lympllkniitsehen in dem Blinddzmn
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| und in dem Ptoeessus Vermifnrmes. Die "Entwiekluug der '1‘onsi11e'n
| |
| und die hlntwieklung der Milz. Arch. f. Anat. u, 'Ph_ysioL Anat. Abt.,
| |
| S. 155-186.
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| LEON, C. 1932 I-Hstegcmése do 1’ebauche splénique ehez les sa.|mo11'1<l(=,s. Arch.
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| Anat. m'1e1'0s., T. 28, pp. 363-393.
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| MINOT, C. S. 1892 Human .}<}mbryology, pp. 4.'l.5—417, Wm. Wood and C0,,
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| New York.
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| M()I.LIER, S. 1909 Die Blutbildung in der ombryonale Leber des Me-nsehen und
| |
| die Wirbeltiere. Arch. 1’. mikr. Anat., Bd. '74, S. 474-524.
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| ML"L.Lr:R, W. 1870 The Spleen. Stricker’s Manual of Human and Comparafive
| |
| llistelogy, pp. 349-364. Trans. by Power. Sydenham Soc-iety, Londonl.
| |
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| 'L\'AKAJ1M‘A, A. 1929 'CT1>er die Mm-phngenese der Milz V011 Mega1<.ubu.traeh11s
| |
| Japonieus. 14‘01ia. Anat. .Tapon., vol. 17, pp. 93-112.
| |
| | |
| ~ -——- —--- 1192b Zur 1\1orphologie der M112 von liynobius Fusells. Folia. Anat.
| |
| Japun., vol. 17, pp. 305-323.
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| | |
| O.\'o, K. 1930 Untersuehungen iibcr die Entwi‘cklu11g der n1esch11'ehen Milz.
| |
| Zeitschr. ‘E. Zellfnrseh. 11. mikr. Anat., Bd. 10, S. 573-603.
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| | |
| Rmroxu), M 1908 The development of the spleen. (I. Anat. and Physiel., vol. 49,
| |
| pp. 289-301.
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| SABIN, F. 1912 The development of the spleen. Manual of Human "Embryology.
| |
| Keibel and Mall, vol. 2, pp. 745-751. J. B. Lippincott 00., "Philadelphia.
| |
| | |
| SCAMMON, R-. E. 1915 The histogcnesis of the selaehian liver. Am. J. A1mt.,
| |
| vol. 17, pp. 245 -315.
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| | |
| S(711o'1"r, E. 1919 Morphologische uud experimcntelle Untersuo11ungen iiher
| |
| Bedeutung und Herkunft der Zellcn der serfisen 116111011. Arch. f. mikr.
| |
| Anan, Bd. 74, S. 14.3—‘>14.
| |
| | |
| ’l.'HIEI., G. AND HAL 1)mvxr.v 1921 The development of the mammalian spleen
| |
| with speeial refm-euee to its hemopoietit-. activity. Am. J. Annf-., vol.
| |
| 28, pp. 279-339.
| |
| | |
| TOLD’1‘, (1. 1889 Zur Anatomic dor Milz. Wiener klin. Wochensch1'., Bd. 2, S. 989.
| |
| | |
| 'I.‘oNK0E‘14*, V". 1900 Die }‘}ntwieklu11g der Milz bei den Amniofen. Arch. 1''. mikr.
| |
| A'r1at., Bd. 56, S. 35)2—<158.
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| | |
| | |
| Plates
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| | |
| 1 The splenie region of a 6—mm. human enibryo showing the relations in the
| |
| dorsal mesogastrium before the spleen appears. There is a local bulging of the
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| mesentery but no condensation. The primitive ooelomic epithelium is a dense
| |
| mantle of cells continuous with the underlying meseneiiynial syneytiuin and with
| |
| the differeiitiaterl mesothelium at the root of the n1esentery_ Ilemaroxylin and
| |
| eosin. Photo X 200.
| |
| | |
| 2 The splenic anlage of a 10—mm. pig leml)ry0 showing the dense local mass
| |
| of cells continuous and morphologically similar h0tl1 with the eoelomic epithelium
| |
| and the adjacent mesenehyme. Wright’s and Giemsa stain. Photo X 550.
| |
| | |
| 3 The splenie anlage of a 12-mm. pig embryo. The cells are a.1'r2111g'e(l in :1
| |
| single layer and a ‘ light zone’ is apparent at some points between the peripheral
| |
| nuclear stratum and the nleseiiehyme. There is no basement membrane and the
| |
| cells at a, b and e are niigratirig into the mesenchyme. The apparent double
| |
| nuclear layer at some points inclioates that the section is not exactly transverse.
| |
| I)elafield’s hematoxylin and azure ll eosin. Photo X 750.
| |
| | |
| 4 Human embryo, 11 mm, showing the early buckling of the dorsal meso,<2;ast1'ium toward the left and the appearance of the splenic vessels in the coneavity of the resulting fold. The splenie anlage is indieatecl by the prorninenee
| |
| at the eoxnexity of the fold as it does not stand out clearly from the adjacent
| |
| dense mesenchyme. The eoelomie epithelium has become a simple eolumnar layer,
| |
| but there is no basement membrane. There is a. well-defined euboidal. layer on
| |
| the concave surface of the mesenteric fold. llematoxylin and eosin. ‘Photo X 200.
| |
| | |
| 5 Human embryo, 13.5 mm. The splenie anlage is a distinct condensation of
| |
| mesenchyme. The overlying eoelomio epithelium has become a low columnar
| |
| layer marked off by a. basement membrane except in a few places (fig. 6). This
| |
| columnar layer is continuous with the cuboidal layers beyond the margins of the
| |
| anlage. Hematoxylin and eosin. Photo X 200.
| |
| | |
| 6 Detail from preceding figure. The (tell me. is being added to the splenio
| |
| Inesenchyme. nm. is a typical mesenchymal nueleus in one of the epithelial cells.
| |
| Photo X 400.
| |
| | |
| | |
| EXPLANATION on FIGURES
| |
| | |
| 7 Pig embryo, 14 mm., showing the forination of the splenie fold in the dorsal
| |
| niesogastrium and the bulging due to the growth of the anlage. The splenie eondensation is distinct from the surrounding niesencliyiiio, particularly in the region
| |
| of the splenic Vessels.
| |
| | |
| 8 Detail froin preceding figure, showing the euhoida.l eoelomie epitheliuin and
| |
| the early formation of the light zone. 4 and 1) indicate cells passing into the
| |
| inesenellyine. Photo X 550.
| |
| | |
| 9 Huinan embryo, 15 mm. The spleen is situated in the convexity of :4, sharp
| |
| be-ml in the 1n(vse.11tory. The hilus is located in the loose iricsenehyme in the
| |
| eoiieavity of this bend. The eoelomie epithelium is a columnar layer completely
| |
| out off from the spleen by :1 basement nnenibrane. Hematoxylin and orange G.
| |
| Plmto X 200.
| |
| | |
| 10 Pig embryo, 22 mm. There is 4, distinct euboidal layer of aoeloniic.
| |
| epithelium sharply mzu'ked off by :1 haseinent. membrane. Delafield’s henmt.ox_ylin
| |
| and azure II eosin. Photo X 550.
| |
| | |
| 11 Pig embryo, 35 mm., showing the persistence of a euboidal type of mesotheliuin over the spleen. De1afie]d’s hematoxylin and azure II eosin. photo X 750.
| |
| | |
| 12 Human embryo, 22 mm. There is a distinct low euhoidal layer of 1Yl(',8()thelium simulating somewhat. the adult, condition. Ilexrmtoxyliii mid eosin.
| |
| Photo X 750.
| |
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| {{Footer}}
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| [[Category:Spleen]][[Category:1930's]][[Category:Historic Embryology]]
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