Let us remember what the word adaptation is really to mean in our discussions: a state of functioning is adapted--a state of functioning must therefore have been disturbed; but as functioning itself, at least in plants, certainly stands in close relations to the medium, it follows that all adaptations are in the last resort connected with those factors of the medium which affect functioning. In being correctives to the disturbances of functioning they become correctives to the disturbing factors themselves. But again, the question seems to arise whether these factors of the medium, when they provoke an adaptation by some change that is followed by functional disturbance, do so in the capacity of “causes” or of “means,” and so it might seem that we have not gained very much so far by our analysis. The reproach, however, would not be quite justified, it seems to me: we indeed have gained a new sort of analytical concept, in the realm of causal concepts in general, by clearly stating the point that adaptations are related directly to functionality, and only indirectly, through functionality, to external changes. By the aid of this logical formulation we now are entitled to apply the term “cause,” in our restricted sense of the word, to every change of the medium which is followed by any sort of adaptation in regard *to itself*. Our definition stated that a “cause” is any one of the sum of necessary factors from without that accounts either for the localisation *or* for *the specification* of the effect, and the definition holds very well in this case. Indeed, the specification of the effect is determined *by* the outside factor in every case of an adaptation *to* it, by the mere *fact* of its being a specific adaptation to this specific factor. We must not forget that in this chapter we are not studying real individual morphogenesis as the realisation of what has been inherited, but that at present we regard morphogenesis proper as an accomplished fact. Morphogenesis proper has laid the general lines of organisation; and now adaptation during the functional life, so to speak, imposes a second kind of organisation upon the first. It is for that reason that the meaning of the word “cause” is now becoming a little different from what it was before. In order to study a little more in detail what has been discovered about morphological adaptation in animals and plants, let us separate our materials into two groups, one of them embracing adaptations with regard to functional changes from without, the other adaptations to those functional changes which come from the very nature of functioning. Almost all of our previous general considerations have applied to the former group, with which we shall now proceed to deal. ADAPTATIONS TO FUNCTIONAL CHANGES FROM WITHOUT[78] [78] Compare Herbst, *Biol. Centralbl.* 15, 1895; and Detto, *Die Theorie der direkten Anpassung*, Jena, 1904. A full account of the literature will be found in these papers.