2242. As the urine is chiefly characterized by the urea and thus by a basic principle; it thus corresponds to the bile, and consequently the kidneys directly to the liver or the lung reversed. 2243. But there is also a sexual branchia in those inferior animals which breathe through the anus, such as many aquatic larvæ. 2244. The remnant of this in the higher animals appears to be the allantois, and in the body itself probably what have been called the primordial kidneys. 2245. The combination of the vascular system with the animal systems is the sense of touch. 3. RESPIRATORY ORGANS. 2246. The respiratory organ is a development of the integument. 2247. The perfect organ of respiration is an air-organ or _lung_; combined with the tegumentary system, it is a water-organ or _branchia_. 2248. There are _dermo-branchiæ_ or the _branchiæ_ proper, as in the Worms, Molluscs, Snails, and Crabs. 2249. Intestinal branchiæ in the Holothuriæ, constituting in the higher animals a _spleen_. 2250. The sexual branchiæ are probably the primordial kidneys. 2251. The branchiæ when united with the osseous system are the branchial arches of Fishes, which subsequently separate into larynx and thyroid gland. 2252. The self-substantial development of the integument into the respiratory organ is a lung. 2253. When united with the vascular system or the vegetative systems generally, the integument forms the tracheal system of Insects. 2254. The tracheæ are spiral vessels as in plants. 2255. The respiratory organ, united with the motor system, is the lung proper, which is situated within the thorax, and covered by ribs. 2256. The proper lung divides also, like the intestine, into two parts, into the cystiform, pharyngeal expansion of the larynx, and into the pulmonic substance, which is equivalent to the stomach, and wherein the analysis of the air takes place. 2257. The trachea, and especially the larynx, is moreover an entire thorax, a ribbed skeleton upon a small and membranous scale. In the larynx, the animal thoracic structure, consisting of ribs and muscles, resides prognosticated. The larynx has originated from the coalescence of branchial arches. The ribs are a repetition of the branchial arches. 2258. The diaphragm is a formation, which admits, by no reasoning from its anatomy, but only genetically, of being explained. Originally, the whole body was only an abdomen, upon the external surface of which the branchiæ were appended. A remarkable instance of this is at once afforded by the Snails, and also the Fishes. As the gills were converted into lungs, a special body or the thorax originated for them, which encroached upon the abdomen. Now, the abdominal wall left between these two cavities, was just the diaphragm. 2259. The diaphragm is not a transverse wall or septum. The idea of such a cross-rail gainsays all sound physiology. It has been the abdominal wall. 2260. The union of the lungs with the nervous system is the nose.