This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
The development of cells of immune system in the individual is called as: 
Select and explain. 
A. Ontogeny, B. Phylogeny, C. Allogeny, D. Heterogeny
A: Ontogeny
Answer: A: Ontogeny 
Explanation: Immunological ontogeny:
The origin and development (=ontogeny) of the lymphocyte system, from its earliest stages to the two major populations of mature lymphocytes: the thymus dependent or T lymphocytes, and the thymus-independent or B lymphocytes.