In preceeding studies, we clarified the histology of the deep cortex of the rat lymph node. It was shown that the deep cortex is made up of basic elements termed “deep cortex units,” some of which are fused to one another into “deep cortex complexes.” Each unit is a semirounded lymphocytic structure, centered on the opening of an afferent lymphatic, contiguous to the peripheral cortex, and bulging into the medulla of a node. Moreover, each unit comprises a “center” and a “periphery,” bearing distinct morphological features. The present work was undertaken to verify whether the histology of the deep cortex of nodes from various species of mammals, currently used for experimental immunology, is comparable to that of the rate. The observations yielded a positive answer to the question.