| 单词 | primitive streak |
| 释义 | > as lemmasprimitive streak primitive streak n. [after German Primitivstreifen ( K. E. von Baer Entwickelungsgeschichte der Thiere (1828) I. 12)] Embryology a thickened band of cells present in the midline of the blastoderm in many vertebrate embryos, from which the mesodermal tissues develop. ΘΚΠ the world > life > biology > biological processes > procreation or reproduction > reproductive substances or cells > [noun] > ovum or ootid > fertilized ovum and parts primitive streak1833 mulberry mass1851 morule1857 morula1875 stirp1875 cytula1876 vegetative pole1876 genoblast1877 mulberry germ1879 parent kernel1879 vegetal pole1881 animal pole1882 amphiaster1885 oosperm1888 segmentation sphere1898 1833Primitive streak [see sense B. 7b]. 1879 tr. E. Haeckel Evol. Man I. 299 In the centre of the primitive streak an even, dark line, the so-called primitive groove, becomes defined. 1939 T. L. Green Pract. Animal Biol. ii. 231 Six hours after incubation begins, note the primitive streak which starts to grow backwards together with the area-pellucida which becomes oval (look at later stages). 1986 A. S. Romer & T. S. Parsons Vertebr. Body (ed. 6) v. 121 An infolding of mesodermal (and possibly endodermal as well) tissues occurs at a peculiarly modified representative of the original blastopore, the primitive streak. < as lemmas |
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