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                  Titre : Philosophical transactions of the Royal society of London. Series B, Biological sciences

                  Titre : Philosophical transactions of the Royal society of London. B

                  Auteur : Royal society (GB)

                  Éditeur : printed by Harrison and sons (London)

                  Éditeur : The Royal society (London)

                  Date d'édition : 1888-1990

                  Type : texte,publication en série imprimée

                  Langue : Anglais

                  Format : application/pdf

                  Droits : domaine public

                  Identifiant : ark:/12148/cb34422226r/date

                  Identifiant : ISSN 00804622

                  Source : Bibliothèque nationale de France

                  Relation :

                  Description : Variante(s) de titre : Philosophical transactions of the Royal society of London

                  Description : Variante(s) de titre : Philosophical transactions of the Royal society of London

                  Description : Périodicité : Irrégulier

                  Description : Etat de collection : 1888 (vol. 178)-1939

                  Provenance :

                  Date de mise en ligne : 15/10/2007

                  First issue for the year 1908 Previous issue 1908 (VOL199). Next issue Last issue for the year 1908
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                  Rechercher dans ce périodique

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                  The portions of the blastoderm containing the streak and its environment were
                  removed for sectioning, double-embedded in cedar-oil-celloidin and paraffin, and eut .`
                  in series of 10 micron sections. Their examination showed that a primitive knot was
                  in fact présent ̃ at some distance from. what proved to be the anterior end ôf the
                  primitive streak (cf. text-fig. 7) just as we had previously found to be the case in
                  Spécimens D and DD. It was situated pretty close to the eut edge of the
                  hemispherieal segment in which it lay. It had escaped détection partly, no doubt,
                  owing to the difficulty of thoroughly investigating the margin of the hémisphère, but
                  partly also from the fact that the cèllular tissue of the knot in this specimen was less
                  permeated by yolk spherules, and was therefore less opaque, than was the case in
                  other specimens of the. stage. At all events we failed to detect the knot on surface
                  examination, and its apparent absence nonplussed us not a little, so that its later
                  discovery in the section-séries came as a welcome relief from our perplexity.
                  The fourth spécimen in our possession, représentative of the stage under, notice, is
                  designated in our list as Spécimen Y. The cireur. istances of our access to this egg
                  are somewhat interesting. Somefew years ago one of us received from the Australian
                  Muséum a spirit-specimen labelled as the pregnant left utérus of an Ornithorhynchus
                  shot on thé Omlgegorïg River, N.S. W., on Augusfc 11, 1884, by Mr. A. G. Hamilton,
                  now of Mount Kembla, N.S.W.

                  A spirit-specimen of '20 years' standing had not appeared a promising aid to
                  research, especially in view of the delicate character of the egg likely to be found
                  in an only very moderately enlarged uterus. We decided, liowever, to open up the
                  specimen by a longitudinal eut through the utérus with a sharp razor. There was
                  then 'disclosed ^itliin thé utérine canal, and in intimate apposition with Its walls, an
                  egg measuring 12 by 10 millims., the egg itself being divided into two soniewhat
                  unequal hemispheroidal segments. It appeared to be in a condition of excellent
                  préservation, and contained a quantity of loose and easily evacuated yolk-material.
                  Both segments were then stereophotographed with the aid of the Braus-Driiner
                  caméra. A stereograph of thé deeper of the two segments, in situ in the uterus, is
                  reproduced in fig* 6, Plate 4. In this stereograph the primitive knot may be
                  recognised as a small white spot in the better-lighted area of the concave segment.
                  It was decidedly more prominent here than in Spécimen DD, formerly. described.
                  We sought in vain for indications of the primitive streak in the vicinity of tbe knot.
                  On the opposite segment of the egg, however, there was discovered, with some
                  difficulty, a tolerably lëngthy portion of a primitive streak. This measured
                  4;9 millims. in length and ran obliquely to the eut edge of the segment which inter-
                  sected it very obliquely. This caudal segment of thé primitive streak was found to
                  end posteriorly, after widening slightly, by joining the concavity of a crescentic
                  thickening which extended across, at right angles to the course of thé streak, for a
                  distance of 128 millims. The apparent breadth of the 'streak itself', a short distance
                  in front of its caudal termination, was about 0'2 millim.

                  Source: / Bibliothèque nationale de France


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