Correct! The primary lymphoid organs include the bone marrow and thymus, while secondary lymphoid organs include: spleen, lymph nodes, and MALT. Dense aggregations of MALT can be found in:

Periarteriolar lymphoid sheath (PALS) surrounds the central arteriole playing an important role in immunological surveillance.

CA = central arteriole; PALS = Periarterial lymphatic sheath This is immunohistochemistry, staining actin with FITC (green) and Type II collagen with Rhodamine (Red) and DAPI (Blue) for cell nuclei

PALS are formed mainly from: