Our mention of plants leads us to the last of our analytical results. If an animal germ proceeds in its development from a stage *d* to the stage *g*, passing through *e* and *f*, we may say that the whole of *d* has become the whole of *f*, but we cannot say that there is a certain part of *f* which is *d*, we cannot say that *f* is *d* + *a*. But in plants we can: the stage *f* is indeed equal to *a* + *b* + *c* + *d* + *e* + *a* [Transcriber’s note: probable typo for *f*] in vegetable organisms; all earlier stages are actually visible as parts of the last one. The great embryologist, Carl Ernst von Baer, most clearly appreciated these analytical differences between animal and vegetable morphogenesis. They become a little less marked if we remember that plants, in a certain respect, are not simple individuals but colonies, and that among the corals, hydroids, bryozoa, and ascidia, we find analogies to plants in the animal kingdom; but nevertheless the differences we have stated are not extinguished by such reasoning. It seems almost wholly due to the occurrence of so many foldings and bendings and migrations of cells and complexes of cells in animal morphogenesis, that an earlier stage of their development seems *lost* in the later one; those processes are almost entirely wanting in plants, even if we study their very first ontogenetic stages. If we say that almost all production of surfaces goes on outside in plants, inside in animals, we shall have adequately described the difference. And this feature again leads to the further diversity between animals and plants which is best expressed by calling the former “closed,” the latter “open” forms: animals reach a point where they are finished, plants never are finished, at least in most cases. I hope you will allow that I have tried to draw from descriptive and comparative embryology as many general analytical results as are possibly to be obtained. It is not my fault if there are not any more, nor is it my fault if the results reached are not of the most satisfactory character. You may say that these results perhaps enable you to see a little more clearly and markedly than before a few of the characters of development, but that you have not really learnt anything new. Your disappointment--my own disappointment--in our analysis is due to the use of pure description and comparison as scientific methods. THE LIMITS OF PURE DESCRIPTION IN SCIENCE We have analysed our descriptions as far as we could, and now we must confess that what we have found cannot be the last thing knowable about individual morphogenesis. There must be something deeper to be discovered: we only have been on the surface of the phenomena, we now want to get to the very bottom of them. Why then occurs all that folding, and bending, and histogenesis, and all the other processes we have described? There must be something that drives them out, so to say.