Growth and differentiation of rat egg-cylinders under the kidney capsule

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Abstract
Two groups of embryonic shields were transferred under the kidney capsule, on days and 9 of normal pregnancy. The first group was without mesoderm and the second one with well-formed mesoderm. Random-bred and inbred Fischer rats were used. Killed and fixed 15 and 30 days after the operation, the grafts looked like teratomata with well-differentiated tissues. Differentiation was the same in embryos explanted at and 9 days, and from the two strains of rat. In order to study the growth potential, transfers within and between each strain of rat were carried out. A difference in weight was found 15 days after the operation among some series. This was not observed 30 days after the transfer. Although the grafts in random-bred rats were larger than in the inbred Fischer strain, factors other than the immunological influence were invoked for the explanation of the initial difference in growth. Long-term grafts were studied only in the inbred strain. Two, 4 and 6 months after the operation all well-differentiated tissues were still present. The amount of growth was very variable within each series, but no graft was found totally resorbed. Only in the largest graft, 6 months after the operation, large masses of cells were found which seemed to be undifferentiated.