Lymph node. Coloured scanning electron micrograph (SEM) of a section through part of a lymph node. The lymph nodes are rounded bodies of lymphatic tissue found at intervals in the course of lymphatic vessels. They are mostly found in the neck, groin and armpit areas. Here, the lymph node is composed of a connective tissue meshwork of reticulin fibres (yellow, thin). In amongst the fibres are white blood cells (green and red spheres) in various stages of development. Lymphocyte and monocyte white blood cells are produced in the lymph nodes. The lymph nodes act as filters, preventing microorganisms from entering the bloodstream. Magnification: unknown.