In examining the origin of the individual members of the vegetative sphere, of which we have already observed that the formation from without toward the internal parts, namely from the umbilical cord into the cavity of the stomach, presents the organs of digestion (as the internal nourishing root of the animal) and the bowels,—we find that in the progress of organization new organs are formed for the functions of respiration and secretion, to correspond to those of nutrition and absorption. The function of respiration indicates the connexion of the individual organism with the atmosphere, as on the other hand the absorption of grosser matter indicates its connexion with the earth by the root.
As long as the fœtus is inclosed in the placenta it can have no immediate connexion with the terrestrial organism, but maintains rather a reciprocal action with the maternal organism, as is seen in its manner of breathing, which is originally performed through the integuments of the egg (see p. 247). But since it is necessary that an independent organ of respiration be prepared for the time when the fœtus leaves the maternal body and the integuments die away, we find the external surface of the fœtus itself (the skin) developed with its continuation (the internal organs of respiration). The vascular system (hitherto the connecting medium between the fœtus and the integuments of the egg, see p. 247), then becomes the connecting medium between the organs of digestion, respiration, and secretion. The organs of secretion, however, may in a certain respect be considered as a repetition of the organs of respiration, since the evaporation and secretion of gases form a prominent part in the process of respiration. The plant develops, besides the organs of general assimilation and secretion, those of generation: a similar development takes place in the animal also, and precisely at the point where the germ of the fruit is developed in the plant, at a point which is therefore analogous to the insertion of the stamen in the flower; in other words, at the insertion of the umbilical cord into the abdominal cavity, which in the first stage of formation, where we observe the embryo with its pointed lower extremity attached to the inner surface of the egg, is the basin that incloses the genitalia as the calyx does the fruit-germ.
After having considered the transition of the form of the plant into that of the animal, it remains for us now to examine the peculiarity of the active living principle of the animal, in order to ascertain how far this is derived from the active living principle of the plant. But we must first carefully observe, that if we were right in considering (page 239) the chief end of the active living principle of the plant to be its formation, the first active living principle in the animal likewise must be a tendency to acquire individual existence. The whole animal body, as far as regards nutrition, growth, secretion, and its being engaged
