This feeling of frustration, so incisively conveyed by these considerations by P. Medawar, pervaded in the forties the field of experimental embryology which had been enthusiastically acclaimed in the mid-thirties, when the upper lip of the amphibian blastopore brought this area of research to the forefront of the biological stage. ❋ Unknown (1986)
This brain and spinal cord did not arise from the transplanted cell material, but from the presumptive ventral epidermis whose course of development was thus altered by the presence of the blastopore. ❋ Unknown (1965)
Upper blastopore lip still engaged in invagination was implanted in a different orientation in relation to the host embryo - crosswise and opposite to the orientation of the later primary primordia. ❋ Unknown (1965)
Then along the line of invagination, i.e. the primitive orifice or blastopore, runs the outer layer of cells or ectoderm into the two invaginated layers, the mesoderm (originating from the marginal zone), and entoderm ❋ Unknown (1965)
In order to test this, a portion of upper blastopore lip at the beginning of gastrulation (head-organizer) and one from an advanced and mature gastrula (trunk-organizer) were transplanted in the same place in an early gastrula, i.e. at the site where the lower blastopore lip would later develop; this was done also at different sites - in the head and trunk areas. ❋ Unknown (1965)
From this Spemann could ascertain that the blastopore had an organizing influence on its environment. ❋ Unknown (1965)
The primordium of the central nervous system originates in the ectoderm of the dorsal surface, starting from the blastopore and coming forward as a thickened plate shaped like a shield with its anterior half broader than its posterior. ❋ Unknown (1965)
Now, when random samples were taken from the whole surface of the gastrula and transplanted in this way in an indifferent place it became apparent that a limited area, namely the region of the upper and lateral blastopore lip did not conform. ❋ Unknown (1965)
Spemann then transplanted the anterior lip of the blastopore of an embryo into the ventral side of another embryo it grew a new brain and spinal cord. ❋ Unknown (1965)
Then in front of this blastopore there arise from the ectoderm the primordia of the brain and spinal cord. ❋ Unknown (1965)
In the course of gastrulation the invaginating material is rolled inwards around the upper lip of the blastopore. ❋ Unknown (1965)
_Peripatus_, [449] Sedgwick was struck with the close resemblance existing between the elongated slit-like blastopore of this form (giving rise to both mouth and anus), with its border of nervous tissue, and the slit-like mouth of the Actinozoan (functioning both as mouth and anus), round which, as the Hertwigs had shown, there lies a special concentration of nerve cells and nerve fibres. ❋ Unknown (N/A)
He denied that the invagination opening (which he named the blastopore) represented the primitive mouth, [443] holding that this was typically formed by an "inruptive" process at the anterior end of the planula, which led to the formation of a "stomodæum." ❋ Unknown (N/A)
He by no means rejected the theory that the Gastræa, "however evolved, was a primitive form of the Metazoa," but, having regard to the great variations shown in the relation of the blastopore to mouth and anus ❋ Unknown (N/A)
Why, for instance, should the blastopore so often appear as a long slit, closing by concrescence, unless this had been the original method of its formation in remote Coelenterate ancestors? ❋ Unknown (N/A)
A sagittal section of approximately this stage, shown in figure 1A, represents the foregut, _fg_, as a shallow enclosure of the anterior region of the entoderm, while the wide blastopore, _blp_, connects the region of the hindgut with the exterior. ❋ C. M. [Illustrator] Reese (N/A)
The circular blastopore in the frog in later years often went by the name of the anus of Rusconi. ❋ Unknown (N/A)
In other respects Sedgwick's speculations link on more closely to the Gastræa theory, for one of his main contentions is that the blastopore or ❋ Unknown (N/A)
Kowalevsky, [452] who had also sketched a theory of the common descent of these two phyla from an ancestral form in which the nervous system encircled the blastopore. ❋ Unknown (N/A)
The characteristic relation of the central nervous system to the blastopore in Annelida and Vertebrates had already been pointed out by ❋ Unknown (N/A)
