So what exactly do we mean? Well, when the embryo is developing inside the uterus of the mother to actually form the fingers on the hand and the toes on the feet, apertosis must take place naturally between the regions on the fingers to actually form the fingers. So the reason we go from this to this is because of apertosis that takes place during normal embryological development. Now, what about development of our immune system? Well, remember, T cells, also known as T lymphocytes, mature and develop inside the thiamis. So what happens inside the thiamis, which is an organ found in this section of the body inside the thiamis, those T lymphocytes are tested against self antigens.