beings in diagrammatic form, each part of the complete animal or plant being represented by some part of a chromosome, though of course not physically resembling it. And we thus strike on the very curious and startling fact that, as far as we can see, _every_ cell in every organism throughout the world of life contains all the elements of the whole being to which it belongs, and is, potentially, that being.[39] All the higher organisms possess two kinds of cells—reproductive cells which have the faculty of fusing together to reproduce their kind, and ‘somatic’ or body cells, which, although they all originate in a reproductive cell, multiply only by division, and have the function of forming the various parts of the bodily structure. Of the nucleus of a germ cell “we cannot say that it differs in any essential or definite way from the nucleus of any other cell.”[40] All possess the chromatin or hereditary substance of the organism, though, according to Boveri, the germ cells alone receive _all_ the chromatin of the parent cell, the derived somatic cells having to part with some of it.[41] There may be some distinction, though on what it may be based it is at present impossible to say, between cells that are capable of developing into a complete organized creature and those that are not. Every somatic cell is doomed to perish, but every reproductive cell now upon the globe is united, not metaphorically, not by a chain of successive originations or impulses, but by actual identity of substance, with the first beginnings of protoplasmic life in the abyss of time; and it has before it a potential immortality commensurate with life itself. It is not, as used to be thought, a physiological product of the organism in which it dwells; it is a part of the original reproductive cell from which that organism sprang. To understand these conceptions we must now study the phenomena of reproduction in the light of recent discoveries.