Morphology and movement of splenic reticulum cells of the normal adult mouse were observed in the growth zone of tissue culture by phase contrast microscopy and 16 mm micro-cinematography. 1) For the vital observation of these cells, rectangular cover slip method proved satisfactory. 2) In tissue culture of normal mouse spleen, lymphocytes appeared initially untill 24 hours, follwed by some types of reticulum cells which increased after 24 to 48 hours of culture, and finally fibroblasts increased in the growth zone. 3) According to the morphology, function and degree of maturation, these reticulum cells could be classified into three groups; Ⅰ, Ⅱa, Ⅱb, Ⅲa and Ⅲb. There were intermediate types between these cells and type Ⅰ reticulum cells matured into type Ⅱ and Ⅲ reticulum cells. 4) Type Ⅱa reticulum cells possessed multiple pseudopods and showed active migratory movement, their nucleus locating in the forwarding part of the cytoplasm.