(embryology) one of the processes of gastrulation, in which certain cells migrate to the inside of the embryo and distribute themselves under its surface layer.
entry into a country for the purpose of permanent or temporary residence by citizens of other countries.
Immigration has economic causes (the importation of a labor force or the entry into countries with more favorable working conditions, a higher standard of living, etc.), military causes (the capture of foreign lands and their military colonization), and political causes (flight from political, national, racial, religious, and other types of persecution, the exchange of national minorities among states, etc.).
Immigration has played a very important role in settling certain parts of the world and in forming the population of many of the world’s countries. Immigration has a vital influence on population dynamics; its demographic consequences are conditioned not only by the number of immigrants but also by their sex and age structure—there is a noticeable predominance among immigrants of young and middle-aged people and of men. Immigration leads to a mixing of various ethnic groups in the population, as a result of which new nations and nationalities are formed.
Immigration is characteristic of all historical periods. An enormous influence on the formation of the population of Eurasia was brought about by the migrations that have taken place during the past 2,000 years, such as the Great Migration of peoples throughout Europe (fourth to seventh century) and the migrations connected with the Arab conquests (seventh and eighth centuries) and with the expansion of the Turks and Mongols (11th to 17th century). The era of the great geographical discoveries (from the mid-15th to the mid-17th century) laid the foundation for the extensive growth of intercontinental migrations, for the most part from Europe to other parts of the world, primarily to America and Australia.
During the 20th century the pace of migration has not slackened, although the migrations themselves have acquired a different aspect in a great number of instances, such as the enormous population shifts connected with the two world wars; the resettlement of more than 16 million persons brought about by the partition of British India into two independent states—India and Pakistan; and the migrations connected with the resettlement of Jews in Israel, as well as the flight and ousting of Arabs. At the same time there are still significant shifts of population for economic reasons. Since World War II (1939–45) the immigration of a labor force into the developed countries of Western Europe has taken place on a wide scale (the number of such immigrants has reached 8 million, including 3.4 million to France, 2 million to the Federal Republic of Germany, 1 million—that is, 16 percent of the country’s population—to Switzerland, and so forth). The countries that are supplying the immigrants are Spain, Italy, Portugal, Greece, Turkey, and the countries of North Africa.
S. I. BRUK