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.
B lymphocytes are powerless to penetrate the cell so the job of attacking these target cells is left to T lymphocytes. T lymphocytes are cells that are programmed to recognize, respond to and remember antigens. T lymphocytes (or T cells) contribute to the immune defenses in two major ways.