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.
The B cells actually produce specific antibodies to specific infectious microorganisms, while T cells kill infectious microorganisms by killing the body cells that are affected. In addition, T cells release chemicals, called lymphokines, which trigger an immune response to combat cancer or a virus, for example.