length in the æsthetic part of my chief work.[239] [238] As is likewise his capacity for escaping from his pursuers; for in this respect all the four-footed mammalia surpass him. [Add. to 3rd ed.] [239] [See Third Book of the W. a. W. u. V.; later also, in my "Parerga," vol. ii. §§ 50-57 and § 206. (§§ 51-58, and § 210 of the 2nd edition.)] Now, after all these reflections upon the precise agreement between the will and the organisation of each animal, if we inspect a well-arranged osteological collection from this point of view, it will certainly seem to us as if we saw one and the same being (De Lamarck's primary animal, or, more properly, _the will to live_) changing its shape according to circumstances, and thus producing all this multiplicity of forms out of the same number and arrangement of its bones, by prolonging and curtailing, strengthening and weakening them. This number and arrangement of the bones, which Geoffroy de St. Hilaire[240] called the anatomical element, continues, as he has thoroughly shown, in all essential points unchanged: it is a constant magnitude, something which is absolutely given beforehand, irrevocably fixed by an unfathomable necessity--an immutability which I should compare with the permanence of matter in all physical and chemical changes: but to this I shall soon return. Conjointly with this immutability of the anatomical element, we have the greatest susceptibility to modification, the greatest plasticity and flexibility of these same bones with reference to size, shape and adaptation to different purposes, all which we see determined by the will with primary strength and freedom according to the aims prescribed to it by external circumstances: it makes out of these materials whatever its necessity for the time being requires. If it desires to climb about in trees, it catches at the boughs at once with four hands, while it stretches the _ulva_ and _radius_ to an excessive length and immediately prolongs the _os coccygis_ to a curly tail, a yard long, in order to hang by it to the boughs and swing itself from one branch to another. If, on the other hand, it desires to crawl in the mud as a crocodile, to swim as a seal, or to burrow as a mole, these same arm-bones are shortened till they are no longer recognisable; in the last case the _metacarpus_ and _phalanges_ are enlarged to disproportionately large shovel-paws, to the prejudice of the other bones. But if it wishes to fly through the air as a bat, not only are the _os humeri_, _radius_ and _alnus_ prolonged in an incredible manner, but the usually small and subordinate _carpus_, _metacarpus_ and _phalanges digitorum_ expand to an immense length, as in St. Anthony's vision, outmeasuring the length of the animal's body, in order to spread out the wing-membrane. If, in order to browse upon the tops of very tall African trees, it has, as a giraffe, placed itself upon extraordinarily high fore-legs, the same seven _vertebræ_ of