390 BIOLOGY. 



Spleen. 



2238. As opposed to the liver, the arterial system also 

 develops itself upon the intestine as a respiratory or 

 branchial organ. These intestinal branchiae are found 

 in several of the lower organized animals, especially in 

 the Holothuriae and Aphroditse. 



2239. In the higher animals they are aggregated into 

 a special organ, through which the gastric juice obtains 

 oxygen ; this is the spleen. The spleen is the branchia 

 of the stomach ; it has therefore no excretory duct and 

 requires none. 



2240. Lastly, the salivary glands also in the mouth 

 as well as in the duodenum, the abdomino-salivary glands, 

 and even the odoriferous glands on the rectum, such as 

 the castor- and civet-pouches, are complications of vessels 

 with intestinal ramifications. 



C. VASCULAR ORGANS OF THE SEX. 



Kidneys. 



2241. The vascular organ of the sexual system is the 

 kidneys. 



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 larvae. 



2244. The remnant of this in the higher animals ap- 

 pears 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. 



