primitive streak


: an elongated band of cells that forms along the axis of a developing fertilized egg early in gastrulation and that is considered a forerunner of the neural tube and nervous system

Examples of primitive streak in a Sentence

Recent Examples on the Web Lewis Wolpert In 1990, following reports from the U.S. Department of Health, Education and Welfare and the U.K. Warnock Committee years earlier, many countries decided that the formation of the primitive streak at 14 days should mark the limit for how long human embryos could be sustained in vitro. Philip Ball, Quanta Magazine, 13 June 2023 Laws limiting embryo research to either 14 days or formation of a structure called the primitive streak exist in several countries, including the United Kingdom, Sweden, and South Korea. Kelly Servick, Science | AAAS, 26 May 2021 In that transition, the embryo forms a furrow called the primitive streak and folds inward on itself while cells mature into different lineages that will later give rise to all the organs and tissues of the body. Kelly Servick, Science | AAAS, 23 May 2018

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'primitive streak.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


translation of German Primitivstreifen

First Known Use

1833, in the meaning defined above

Time Traveler
The first known use of primitive streak was in 1833

Dictionary Entries Near primitive streak

Cite this Entry

“Primitive streak.” Dictionary, Merriam-Webster, Accessed 22 May. 2024.

Medical Definition

primitive streak

: an elongated band of cells that forms along the axis of an embryo early in gastrulation by the movement of lateral cells toward the axis and that develops a groove along its midline through which cells move to the interior of the embryo to form the mesoderm

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