If we ask how these animals are nourished, in which no digestive apparatus can be distinguished, the question is difficult to answer. It is thought that they are nourished by simple absorption, and by absorption only. In the interior of the gelatinous mass which constitutes the animals, however, granules and microscopic portions of vegetables are frequently discovered. "We can conceive," says Dujardin, "how these objects have penetrated to the interior, if we remark, on the one hand, that in creeping on the surface of the glass, to which they adhere very exactly, the _Amœbæ_ can be made to receive, by pressure, foreign substances into their own bodies, by means of the alternate contraction and extension of the various parts natural to them, and, on the other hand, that the gelatinous mass is susceptible of spontaneous depressions--here and there near to or even at the surface of the spherical cavities, which successively contract themselves and disappear in connection with the strange body which they have absorbed." The _Amoebæ_ are often observed to be tinted red or green; this arises from the special colouring matter which has been absorbed into its mass. The question arises, How do these creatures, so simple in their organization, propagate their species? We believe that they are chiefly multiplied by parting with a lobe, which, in certain conditions, is enabled to live an independent existence, and develop itself, thus forming a new individual. This is what naturalists term generation by division--_fissiparism_ or _fission_. The absence of a nutritive and reproductive apparatus in the _Amoebæ_, and the want of stability in their forms, explain how nearly impossible it is to characterise as species the numerous individuals daily met with in infusions of organic matter in stagnant water. In order to distinguish some of the groups, Dujardin bases his descriptions upon their size and the general form into which they expand. We shall be able to form some idea of the appearance of these beings, rendered mysterious by their very simplicity, by throwing a glance upon the two accompanying figures (Figs. 12 and 13), borrowed from the Atlas of Dujardin's great work, "Les Zoophytes Infusoires," which we shall have occasion to quote more than once. We have said that the _Amœbæ_ change their form every few moments under the eyes of the observer. Fig. 13 represents the changes of form through which they pass, according to Dujardin, when examined under the microscope. [Illustration: Fig. 12. Amoebæ princeps (Ehrenberg), magnified 100 times.] [Illustration: Fig. 13. Various forms of Amoebæ diffluens (Müller), magnified 400 times.]