While the tadpoles of competing species may complete metamorphosis in as little as just a few short months, Bullfrog tadpoles can remain in the same state for as long as one to two years before they actually become adult frogs.
Two types of white blood cells called lymphocytes are vital to the specific immune response. Lymphocytes are produced in the bone marrow, and mature into one of several subtypes. The two most common are T cells and B cells. An antigen is a foreign material that triggers a response from T and B cells.
They are B lymphocytes (B cells) and T lymphocytes (T cells). B cells. B cells develop from bone marrow stem cells in adults. When B cells become activated due to the presence of a particular antigen, they create antibodies that are specific to that specific antigen. cells. T cells develop from liver or bone marrow stem cells that mature in the thymus. These cells play a major role in cell mediated immunity. T cells contain proteins called T-cell receptors that populate the cell membrane.