KEY WORDS: mouse, regulative development, chimaerism, cell lineage, fertilization The beginnings: XIX century -1939Poland lost independence in the XVIII century after she was partitioned between Russia, Prussia and Austria from 1772 to 1795. In the times that followed, many Polish scientists studied and often lived abroad, and many foreigners came to work in Polish academic institutions. In 1816 Alexander I, the Emperor of Russia and the usurper King of Poland, granted permission for the establishment of Warsaw University. The University followed the tradition of three earlier institutions of higher education: Collegium Nobilium, opened in 1766, the School of Law (founded in 1808) and the School of Medicine (founded in 1809). The University still bears the emblem described as "an ancient Polish eagle with a crown, with spread wings, a palm frond in its left claws and laurel branch in its right, the symbols of patient diligence and honour, surrounded by five stars representing its five academic faculties". These faculties were theology, law, medicine, philosophy, and the liberal arts. After the fall of the November 1830 uprising, in which a majority of students had participated, the University was closed in 1831. In 1857 there was a brief period of Int. J. Dev. Biol. 52: 121-134 (2008) +48-22-55-41-210. e-mail: akt@biol.uw.edu.pl # Note: This article is not a review of the principle interests of this Department, and therefore, we quote other authors very selectively, for instance, when they carried out concurrently similar studies, or when their studies are essential for the understanding of the rationale and/or implications of our experiments. liberalization that resulted in the opening of the Main School (Szkola Glowna) with the departments of medical-surgical, law and administration, philological-historical, and mathematics-physics. The Main School was closed in 1869, on the wave of increasing oppression and russification after the fall of the second, the January 1863 uprising. However, in the short period of the existence of the Main School as many as three thousand students graduated and the School had great impact on the development of Polish science and culture. In 1870, the Russian Imperial University was opened in Warsaw. The majority of faculty teachers were Russians and the official (teaching) language was Russian. Steadily the University expanded: new buildings were constructed; academic potential increased and precious zoological and botanical collections were created.The Department of Comparative Anatomy was founded in 1870. It was headed by Russian scientists: Mitrofan Ganin (1870-84), Mitrofan Uljanin (1884-1888) and Pawel Mitrofanow (Mitrophanow) . Mitrofanow ( Fig. 1) was an outstanding avian embryologist working mainly on early embryos; in papers published in 1895 and 1899, he presented evidence that 122 A. Tarkowski et al. which in 1918 -when Poland regained independencebecame one of the first legally functioning Polish national institutions. Soon, many distinguished specialists and...
Hind guts of 9½-day mouse embryos were transplanted into the posterior part of the coelomic cavity of 2½-day chick embryos. The hosts were sacrificed after 1-7 days and the mouse primordial germ cells (PGCs) in the graft and in the surrounding host tissues were searched for by means of the histochemical technique for alkaline phosphatase. Altogether 94 grafts were examined. During the first 3 days of intracoelomic development of the graft accumulations of mouse PGCs close to the mesonephros, the mesentery or the gonad of a chick embryo were observed in 26 out of 51 cases. In 12 grafts single PGCs crossed the boundary between the host and the graft and settled in host tissues such as the mesonephros, the mesentery or the gonad. After 3 days mouse PGCs are no longer visible in the chick tissues. However, the number of PGCs in the grafts also gradually decreases and from the 4th day onwards many of the grafts contain no PGCs. The ability of mouse PGCs to survive extragonadally, even in the embryonic hind gut, is thus limited. In some of the 4- to 7-day-old grafts PGCs occur on the periphery of the graft in the form of single aggregations. From the 6th day the only PGCs which survive are those in aggregations. The experiments indicate that the gonads, together with adjacent tissues (mesonephros, mesentery) of a chick embryo are attractive to mouse primordial germ cells and that the hypothetical attractive substance is not species specific.
Suggestive evidence for the extragonadal origin of germ cells in birds was first presented by Swift (1914), who described primordial germ cells in the chick embryo at as early a stage as the primitive streak. According to Swift, primordial germ cells are originally located extra-embryonically in the anterior part of the blastoderm and occupy a crescent-shaped region (‘germinal crescent’) on the boundary between area opaca and area pellucida. Swift also found that primordial germ cells later enter into the blood vessels, circulate together with the blood throughout the whole blastoderm and finally penetrate into the genital ridges, where they become definitive germ cells. Swift's views have been confirmed in numerous descriptive and experimental investigations. Among the latter, the publications of Willier (1937), Simon (1960) and Dubois (1964a, b, 1965a, b, 1966) merit special attention. Dubois finally proved that the genital ridges exert a strong chemotactic influence on the primordial germ cells.
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