The structure and behavior of living cells is a fascinating, inspiring subject, in its bearing upon evolution; but about evolution- cellular research as yet has uncovered precious little. A popularization of cell theory, whatever revelations are to come, must at present limit itself to the mechanical findings of the laboratory and some general statements about the thought and purpose behind experiment. The author has followed this intention- but too steadfastly. He could easily have lightened the burden of this material with the exciting discoveries in tissue culture, or with studies of the personalities who dominate the cellular field and have established its spirit of inquiry. The book is far too precise and undeviating when it comes to lay interest- and on the other hand it overemphasizes problems in cancer research. The bias is due to the author's own background in cancer work and it will be gratifying and edifying to those connected with this particular phase of research.