1899. When the animal organization, however, ranks upon a higher stage, light, or even air, operates more upon its external wall, but upon its internal, water; thus the antagonism of the two walls is carried out to the utmost degree.
1900. Through the different, ay, opposed processes, the two walls finally adopt another structure. The external becomes denser and harder, on account of the decomposition by light and dessication by air; the internal, however, retains its original structure and consistence. Soft, aqueous, indifferent, and constantly absorbent, it is only a viscous mucus.
1901. In place of an integument of similar tissue throughout, one will originate, whose external tissue is dense and oxydized, but whose internal is loose or spongy, and indifferent. The previously uniform integument will now separate or fall into two distinct layers; into a soft muco-cellular layer, and into a tough coriaceo-cellular layer.
1902. With the last attainable antagonism the layers finally separate; two bladders or cysts, disunited from each other, originate; of these the internal is the mucous, the external the coriaceous cyst.
1903. Now the internal cyst alone is the intestine, the external the cutis or skin.
1904. Intestine and cutis belong to one formation, or to the integument. They pass directly into each other at the mouth and anus. Their structure also is wholly similar.
1905. They are merely distinguished by darkness and light, but more closely by water and air. The intestine is the water-tegument, the skin the air-tegument.
1906. The functions of both are therefore co-related like dissolution is to combustion, along with which the evaporation has been bestowed.
1907. Intestine and skin stand in antagonism with each other.
1908. The first animal, as being sentient integument, is a sac; the first skin is also a sac; an animal around the animal.