"There is, then, nothing wonderful in the supposed industry of the ant-lion (_Myrmeleon formica-leo_), which, having thrown up a hillock of movable sand, waits until its booty is thrown down to the bottom of its funnel by the showers of sand to become its victim; also there is none in the manoeuvre of the oyster, which, to satisfy all its wants, does nothing but open and close its shell. So long as their organization is not changed they will always, both of them, do what we see them do, and they will do it neither voluntarily nor rationally. "This is not the case with the vertebrate animals, and it is among them, especially in the birds and mammals, that we observe in their actions traces of a true _industry_; because in difficult cases their intelligence, in spite of their propensity to habits, can aid them in varying their actions. These acts, however, are not common, and are only slightly manifested in certain races which have exercised them more, as we have had frequent occasion to remark." Lamarck then (chapter vi.) examines into the nature of the _will_, which he says is really the principle underlying all the actions of animals. The will, he says, is one of the results of thought, the result of a reflux of a portion of the nervous fluid towards the parts which are to act. He compares the brain to a register on which are imprinted ideas of all kinds acquired by the individual, so that this individual provokes at will an effusion of the nervous fluid on this register, and directs it to any particular page. The remainder of the second volume (chapter vii.) is devoted to the understanding, its origin and that of ideas. The following additions relative to chapters vii. and viii. of the first part of this work are from vol. ii., pp. 451-466. In the last of June, 1809, the menagerie of the Museum of Natural History having received a Phoca (_Phoca vitulina_), Lamarck, as he says, had the opportunity of observing its movements and habits. After describing its habits in swimming and moving on land and observing its relation to the clawed mammals, he says his main object is to remark that the seals do not have the hind legs arranged in the same direction as the axis of their body, because these animals are constrained to habitually use them to form a caudal fin, closing and widening, by spreading their digits, the paddle (_palette_) which results from their union. "The morses, on the contrary, which are accustomed to feed on grass near the shore, never use their hind feet as a caudal fin; but their feet are united together with the tail, and cannot separate. Thus in animals of similar origin we see a new proof of the effect of habits on the form and structure of organs." He then turns to the flying mammals, such as the flying squirrel (_Sciurus volans_, _ærobates_, _petaurista_, _sagitta_, and _volucella_), and then explains the origin of their adaptation for flying leaps.