Hint:Lymphocytes are a class of white blood cells (WBCs) in the immune system. Since these cells are the main occupants of the lymph, hence the name ‘lymphocyte’.
Complete answer: Lymphocytes are an integral part of the vertebrate immune system and are composed of cell types including natural killer cells, T cells and B cells.
Now, let us look at each option one by one: The Bone marrow is a soft tissue present inside certain bones of the body harboring stem cells for the generation of the red blood cells (RBCs), white blood cells (WBCs) and the platelets responsible for the oxygen transport, immunity and blood clotting respectively. Since lymphocytes are a type of WBCs, they are also formed in the bone marrow. Therefore, this is the correct option.
Pineal body or pineal gland is a small endocrine gland present in the brain. Although all of its functions are not yet known, this gland was found to be responsible for regulating the levels of the hormone melatonin which regulates the sleep cycle in the body. This gland is not at all associated with lymphocytes, therefore, this option is incorrect.
Vermiform appendix or just appendix is a muscular tube like structure attached to the large intestine. Although it is mostly considered a vestigial organ, studies show that it helps in the proper removal of waste from the digestive system, the presence of lymph vessels might help in the removal of pathogens and it might also help in the production of primary response against diseases. There isn’t any evidence of production of lymphocytes in the appendix, hence, this option is incorrect.
The spleen is a fist sized organ present in the abdomen responsible for filtering the blood. This organ is specialized for recognizing and removing old or malformed red blood cells (RBCs) from the circulatory system. Evidence suggesting the formation of lymphocytes in the spleen does not exist. Therefore, this option is incorrect.
Thus, the correct answer is option (A) Bone Marrow.
Note: The B lymphocytes (B cells) are the cells programmed to make antibodies which recognize and attach to foreign bodies infecting the system. These B cells then signal other immune cells in the body to destroy the infecting agent thereby maintaining immunity in the body.