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.
two types of white blood cells that are a part of the immune system: B-lymphocytes form in the bone marrow and release antibodies to fight bacterial infection. T-lymphocytes form in the thymus and attack cancer cells, viruses, and foreign substances.