As the treatise is drawing to a close, this chapter again alludes to the distinction between the life in plants and animals from the presence or absence of sensibility—thus, animals are distinguished from plants by being sentient, as plants are from inanimate bodies by nutrition and growth. Aristotle[1] placed plants immediately after inanimate substances, and says that they are distinguished, generically, by degrees of vitality; that compared with other bodies they appear to be almost alive (σχεδὸν ὥσπερ εὔψυχον); compared with animals, to be inanimate; and that the transition from the one to the other is in an unbroken series. Thus, there are "marine creatures," he says, "which cannot with certainty be ranged among either animals or plants; and sponge has altogether the appearance of a plant." Lamarck[2] has substantively adopted this, as he, too, commences with inanimate things (which, whatever their character, he distinguishes broadly from whatever has life) and then passes to plants, which he distinguishes from animal bodies, by being non-irritable—incapable, that is, of contracting any of their solids, suddenly and repeatedly, while animal bodies are, on the contrary, endowed with contractile power. Cuvier[3] observes, that "living and organised beings have, from the earliest times, been subdivided into animated beings—beings, that is, which are sentient and moveable, and beings which are inanimate; and as these are neither sentient nor moveable, they are reduced to the common faculty of vegetation or nutrition." It is not necessary, then, as Aristotle remarks, that all living beings should be sentient.