But let us never forget that the laws of surface tension only give us the most general type of an arrangement of elements in all these cases, nothing else. A physical law never accounts for the Specific! Capillarity gives us not the least clue to it. As the organic substance, at least in many cases, is a fluid, it must of course follow the general laws of hydrostatics and hydrodynamics, but life itself is as little touched by its fluid-like or foam-like properties as it is by the fact that living bodies have a certain weight and mass. All indeed that has been described may be said to belong, in the broadest meaning of the word, to what is called by Roux “correlation of masses,” though this author originally intended to express by this term only some sorts of passive pressure and deformation amongst embryonic parts as discovered especially by His. We must be cautious in admitting that any organic feature has been explained, even in the most general way, by the action of physical forces. What at first seems to be the result of mechanical pressure may afterwards be found to be an active process of growth, and what at first seems to be a full effect of capillarity among homogeneous elements may afterwards be shown to depend on specialised metabolic conditions of the surfaces as its principal cause.[34] [34] According to Zur Strassen’s results the early embryology of *Ascaris* proceeds almost exclusively by cellular surface-changes: the most typical morphogenetic processes are carried out by the aid of this “means.” As a whole, the embryology of *Ascaris* stands quite apart and presents a great number of unsolved problems; unfortunately, the germ of this form has not been accessible to experiment hitherto. There are other physical phenomena too, which assist morphogenesis; osmotic pressure for instance, which is also well known to operate in many purely physiological processes. But all these processes are only means of the organism, and can never do more than furnish the general type of events. They do not constitute life; they are *used* by life; let it remain an open question, for the present, how the phenomenon of “life” is to be regarded in general.[35] [35] Rhumbler has recently published a general survey of all attempts to “explain” life, and morphogenesis in particular, in a physico-chemical way (“Aus dem Lückengebiet zwischen organismischer und anorganismischer Natur,” *Ergeb. Anat. u. Entw.-gesch.* 15, 1906). This *very pessimistic* survey is the more valuable as it is written by a convinced “mechanist.” *On Growth*.--Among the internal morphogenetical means which are of a so-called physiological character, that is, which nobody claims to understand physically at present, there is in the first place *growth*, which must be regarded as a very essential one.