A critical study of the evidence presented in several recent articles on the development of the lymphatic system

A review of the recent work on the development of the lymphatic system shows that there are marked differences of' opinion on fundamental points and a study of these differences will demonstrate that they center around the question of methods.We differ because our methods differ and therefore it is essential to submit the methods to comparative tests and to understand the limits of error of each one.A t the present time there are at least ten laboratories engaged in solving the problem of the development of the lymphatic system, the investigators being Hoyer, Mierzewski, Polinski, Jolly, Marcus, F. T. Lewis, Huntington, McClure, Stromsten, Allen, Knower, Clark and myself.From this list it can be seen that the majority of modern investigators are basing their work on the theory that the lymphatics are derived from the veins rather than from tissue spaces, that they are lined by true endothelium rather than by undifferentiated mesenchyme cells, and that they are definite vessels with definite walls as sharply differentiated from tissue spaces as are blood capillaries.It is unnecessary to recall the various studies which pointed the way toward the theory of the venous origin of the lymphatics, suffice it to say that there have been three important points established by modern workers: first, that the primary lymphatics are centrally placed lymph sacs, second, that the growth of the