Despite recent successes with the cultivation of mouse and rabbit eggs (references in Austin, 1961, pp. 144–7) techniques for the cultivation of post-implantation mammalian embryos have not hitherto advanced beyond those devised in the 1930's. Jolly & Lieure (1938) obtained development of rat and guinea-pig embryos explanted into homologous serum at stages between primitive streak and a few somites. They report that of their explanted rat embryos 37 per cent, developed an embryonic axis with a rhythmically beating heart, but only 9 per cent, a functioning circulation. None formed limb buds or a functioning allantoic circulation. Nicholas & Rudnick (1934, 1938) appear to have had a similar degree of success with rat embryos explanted into heparinized rat plasma and embryo extract. Waddington & Waterman (1933) explanted rabbit blastodiscs of primitive streak to 3-somite stages on to plasma clots; in the most successful cultures a 6–9 somite embryo was obtained with neural tube and beating heart, but without any blood circulation.

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