On the contrary, it is a very important and fundamental feature of organogenesis that it occurs in separate lines, that is to say, in lines of processes which may start from a common root, but which are absolutely independent of one another in their manner of differentiation. Roux has coined the term “self-differentiation” to denote this phenomenon, and we admit that this term may be conveniently used for the purpose, if only it can be kept in mind that its sense is always relative, and that it is also negative. Suppose a part, *A*, shows the phenomenon of self-differentiation: this means that the further development of *A* is not dependent on certain other parts, *B*, *C*, and *D*; it does *not* mean at all that *A* has not been formatively dependent on some other parts, *E* or *F* at the time of its first appearance, nor does it imply that there might not be many formative actions among the constituents of *A* itself. We indeed are entitled to say that the ectoderm of Echinus shows “self-differentiation” with regard to the endoderm; it acquires its mouth, for instance, as has been shown by experiment, even in cases where no intestine is present at all (Fig. 10); but ectoderm and endoderm both are formatively dependent on the intimate and the material organisation of the blastoderm. It further seems from the most recent experiments that the nerves and the muscles of the vertebrates are independent of each other in their differentiation, but that their fate is probably determined by formative processes in the very earliest stages of ontogeny. [Illustration: Fig. 10.--Pluteus-larva of Sphaerechinus. The Intestine (i) is developed outside instead of inside (by means of raising the temperature); but the mouth (r) is formed in its normal place. S = Skeleton.] The phenomenon of self-differentiation, properly understood, now may help to the discovery of one most general character of all development. If the phenomenon of self-differentiation really occurs in ontogeny in its most different aspects, and if, on the other hand, in spite of this relative morphogenetic independence of embryonic parts, the resulting organism is one whole in organisation and in function, some sort of *harmony of constellation*, as it may properly be styled, must be said to be one of the most fundamental characters of all production of individual form. In establishing this harmony we do nothing more than describe exactly what happens: the harmony is shown by the fact that there is a whole organism at the end, in spite of the relative independence of the single events leading to it.