evidence is provided which suggests that ( i ) embryo-larval urogenital tissues are sites of generation of cells in b lineage , ( ii ) during ontogeny , there is a sequential expression of immunoglobulin isotypes on b cell surfaces , ( iii ) larvae are able to produce the full range of immunoglobulin clases found in adults , and ( iv ) at least two subpopulations of lymphocytes exist in rana pipiens , sig+ and sig- ;
C0007634
cells
C0699040
cell surfaces