Lymph nodes are major sites of bacteria.
  In some amphibian and reptilian species, the lymphatic system has central pumps, called lymph hearts, which typically exist in pairs, but humans and other mammals do not have a central lymph pump
 Bacteria living in biofilms display a complex arrangement of cells and extracellular components, forming secondary structures, such as microcolonies, through which there are networks of channels to enable better diffusion of nutrients

