cavity and mouth_ but the gastrula-stomach and orifice of by hkksew3563rd

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									                  A NOTE ON ENDOTHELIUM.                   391

cavity and mouth, but the gastrula-stomach and orifice
of invagination ; the latter clos.es up, and the pedicle so
formed becomes the rectum, which terminates blindly.
   E. With a good English quarter, or, better, with Hartnack's
10 immersion, and the use of osmic acid, the cilia which
cause the rotation may be seen. They are disposed on an
annular band, the commencing velum.
   F. The annular ridge has nothing to do with the mantle's
margin, but is the velum.
   G. The new in-sinking has no connection with the anus ov
rectum, which latter already is taking shape in the pedicle
of invagination. It is the " shell-gland," a structure com-
mon to many embryo mollusca, but hitherto unrecognised.
   H. The so-called large yelk-spheres are not now first
formed, but have been there all the time, forming the wall of
the invaginated gastrula-stomach. They now undergo im-
portant segregative changes, and present the appearance of
large clear globules, covered in by a fine granular reticulum.
   i. The alimentary canal is from the first bent, the csecal
termination of the rectum lying a little forward, and not
opposite the mouth.
   j . The shell, as an exceedingly delicate membrane on the
surface of the shell-patch (in the centre of which lies the
shell-gland), is observable long before this.
   K. The mouth never pushes forward, but rather becomes
sunk and enclosed by the increasing development of the
border of the velum, where it overhangs the mouth. This
part of the velum forms the subtentacular lobes of the
adult.
   L. It can be seen at a very much earlier period.



A   NOTE on ENDOTHELIUM.        By   JOHN   CAVAFY,     M.D.,
    Assistant-Physician and Lecturer on Physiology at St.
    George's Hospital.
   IN the last number of this Journal 1 there is a paper by
Dr. M. Foster, " On the term Endothelium," in which he
gives various reasons against the further use of this word in
histological terminology. He objects to the word, both
because its etymology is " of the most grotesque kind," and
also on far more important anatomical grounds.
   Much that is brought forward by Dr. Foster is, doubtless,
true; but some portion of his statement must, I think, he
             ' 'Quart, Jouru. ofMic, Sci.,' 1S74, p, 219,
392                       DR. CAVAFY.

 admitted to be mistaken, and he has completely passed over
 some important reasons which exist for maintaining the
 separate terms originally proposed by His.
    In the first place, the word is not quite so ridiculous, ety-
 mologically, as it is represented to be by Dr. Foster. The
 word endotheUum is obviously a contraction of endo-epithe-
 lium, and means an epithelium which is within (IvSov or
 euros, inttts) or internal, i. e. it means precisely what His
 intended to signify, and is only so far a misnomer as (epi-
 thelium is concerned, since it covers "• surfaces of which, one
 great characteristic is that they are devoid of papillee j " but,
 as Dr. Poster says, this extension of the meaning of Ruysch's
 original terms epitheUs (of which epitheUda is the accusative
 case) and epithelia " may be easily allowed." Endothelium
 does not mean " that which is inside a papilla" any more
 than entoderm means ?f that which is inside a skin j " endo-
plast, " that which is inside a formation;" or even entozoon,
 "that which is inside an animal." The real meaning of
 these terms Dr. Foster will, doubtless, admit to bs " a n
 internal skin, formation (nucleus), and animal." The
 etymological objections, therefore, do not hold.
    Let us now consider, shortly, whether the physiological
 differences between epithelium and endothelium are sufficient
 to warrant the use of separate terms.
    Dr. Foster says that endothelium cannot be employed to
 denote the epithelium derived from the mesoblast, " for it
 would then include structures still called epithelium, aod
 differing in no essential characters from the epithelium
 derived directly from the hypoblast." But we should not
 forget that the mesoblastic origin of genito-urinary epithe-
lium may be more apparent than real. Waldeyer1 has sug-
gested that its real origin is most probably from cells of the
epiblast, which have become mixed with those of the meso-
blast at the time of the formation of the primitive groove.
 This view is not, of course, susceptible of actual demonstra-
tion ; but it is known, at any rate, that the mesoblast becomes
closely fused with the epiblast in the region of the axial cord
of His, and then again separates; and that it is after this
separation that the Woiffian and Miillerian ducts are formed.
It is therefore quite possible that the cells lining these
organs and their derivatives may be really derived from the
epiblast. Physiologically, at any rate, they are true epithe-
lium, and not endothelium, i- e. they are concerned with
secretion, which is never the case with endothelium. The
email quantity of fluid which bathes the surface of serous
                1
                  'Eierstook und Ei,' pp. 113—114.
                      NOTE ON ENDOTHELIUM.                             393

 and synovial membranes is a filtration or transudation, not a
 true secretion in the ordinary physiological sense of the word,
 for endothelium never forms glands, whereas a share in gland-
 formation, and, consequently, secretion, is a constant charac-
 teristic of epithelium, whether derived from epiblast or
 hypoblast.
    As Dr. Foster says, continuity " affords no argument
 whatever for classing . . . . together. "We find continuity
 everywhere." But in the case of endothelium we find in one
 most important instance, not only continuity, but something
 more. What takes place in the growth and development of
 capillary blood-vessels and lymphatics ? We have in each
 case a vacuolation and excavation of connective-tissue-cor-
 puscles, whose protoplasm becomes ultimately changed into
 endothelial plates, and we may find every transitional form
 between a flattened connective-tissue-corpuscle occupying
 the lymph canalicular system and the endothelium forming the
 wall of the lymphatic vessel with which it communicates.
• We have here, therefore, to do with convertibility as well as
 continuity; and if Dr. Foster admits that the connective
 tissues form a natural group derived from the mesoblast, of
 which convertibility of one member into another (well seen
 in pathological conditions) is one of the most striking cha-
 racteristics, I do not see how he can exclude endothelium
 from a very close connection and relationship with the
 members of that group. In fact, the most recent researches
 on connective tissues have established a nearly complete
 identity between endothelium and connective-tissue»cor-
 puscles, and this identity is strikingly evidenced by the
 close similarity of the pathological changes which they
 both undergo.1
    Now, in the case of epithelium, not only has no such
 connection with connective tissues been observed, but
 there are marked differences between their respective
 pathological changes. The views of Heidenhain as to the
 continuity of the cylindrical epithelium covering the villa
 of the small intestine with branched connective-tissue-cor-
 puscles in the stroma have been rendered more than
  1 " Les cellules du tissu conjonctif sonb plates, contienuejit des noyaux
gats, et completement impossible de sur les faiaceaux cellule endotlieiiale
  serait
         sont simplement appliquSes
                                    recounaitre une
                                                      du tis3U conjonctif.
isolee de la plupart des cellule* du tissu conjonctif."—Ranvier, art.
"Epithelium," 'Nouveau Dictionnaire de M^deeine,' vol. xiii, p, 687.
   "Les alterations des s6reuses . . . prSsentent une analogie com-
plete avec celles du tiseu coajonctif."—Cornil and Ranvier, ' Manuel
d'Histologie pathologique,' p. 456.
394,                   E. A. SCHAFER.

doubtful by the important observations of Mr. Watney 1 on
intestinal absorption, which he has shown to take place, not
through the epithelium itself, but by pseudo-stomata formed
by processes of connective-tissue-corpuscles, which project
between the epithelium, with which they are never anato-
mically continuous.
   We have, then, in the case of endothelium, not only an
undoubted mesoblastic origin, but a close relationship with
connective tissues; its cells, moreover, never form glands
nor secrete. Epithelium, on the other hand, has a doubtful
derivation from the mesoblast; gland-formation and secretion
are among its most constant and striking characteristics,
and it has absolutely no relationship with the connective
tissues. Notwithstanding, therefore, Dr. Foster's statement
(p. 292) that, " In short, there is no reason why the cells
spoken of as forming endothelium should have a common
title, distinct from the general term epithelium," I must
confess that I am not convinced, but think that the reasons
I have given above are sufficient to render the use of sepa-
rate ' terms at least opportune—" im Interesse physiolo-
 gischen Verstandnisses."



DESCRIPTION of an APPARATUS2 for MAINTAINING a CON-
   STANT TEMPERATURE under the MICROSCOPE. By E. A.
    SCHAFER, Assistant-Professor of Physiology in University
    College, London.
   THE necessity of having the means of conveniently, but at
the same time accurately, maintaining objects, especially the
living tissues, under observation at a uniform temperature
(generally that of the body) becomes more obvious every day.
The existing methods of effecting this are, as a rule, not
sufficiently accurate for exact investigations; and, on the
other hand, the more accurate modes are frequently in-
convenient of application. For example, the apparatus
described by Strieker and Burdon-Sanderson in this Journal
for 1870,—although it is possible by its aid to maintain
a constant temperature under the microscope for a con-
siderable time,—yet requires that there should be a vessel
of water constantly boiling near the observer, and that
 the water in this vessel should be maintained at a uni-
form level, necessitating a supply tube from a cistern, and
             1
               ' Proc. Roy. Soc.,' vol. xxii, p. 293.
             8
               Made for me by Mr, Casella, of 147, Holborn Bars.

								
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