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 cells must interact with Helper T cells, other specialized white blood cells, to initiate antibody production. An important concept is that once activated, memory cells are produced that insure that a more rapid and stronger immune response can be made upon re-exposure to the same pathogen.