from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Embryology The opening of the archenteron.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The opening into the archenteron.
from the GNU version of the Collaborative International Dictionary of English
- n. The pore or opening leading into the cavity of invagination, or archenteron.
from The Century Dictionary and Cyclopedia
- n. In embryology, the aperture of invagination of a blastula or vesicular morula which has become a gastrula; the orifice of an archenteron; the primitive combined mouth and anus of a gastræa-form; an archæostoma. See cut under gastrulation.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the opening into the archenteron
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.
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.
Then in front of this blastopore there arise from the ectoderm the primordia of the brain and spinal cord.
From this Spemann could ascertain that the blastopore had an organizing influence on its environment.
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.
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.
In the course of gastrulation the invaginating material is rolled inwards around the upper lip of the blastopore.
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.
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.
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.