346 BIOLOGY. 



1930. Were intestine and skin entirely separated 

 from each other, each would perish; the former would 

 no longer be oxydized, the latter no longer nourished. 



1931. With their separation they must continue to be 

 attached to each other, and thus undergo eversion at 

 certain points. Thereby tubes originate in the intestine, 

 which pursue their course toward the skin ; in this again 

 tubes, which pass to the intestine. 



1932. A tube, which receives mucus from the intes- 

 tine, air from the skin, and includes both within itself, 

 is a long bladder. A bladder, which conducts mucus 

 to the skin and air to the intestine, is a Vessel, a vein. 



a. Unclosed Vascular System. 



1933. The vessel has, in virtue of its essence, two ex- 

 tremities, an air-extremity, which is polar, and a water- 

 extremity, which is indifferent. Every vessel has been 

 rooted in two systems, in the intestine and skin, and is 

 subservient to both. 



1934. The vessel is no longer a something single, 

 like the last-mentioned or preceding cysts, but double. 

 Every vessel hath two poles. 



1935. The organization necessarily produces two kinds 

 of vessels. A vessel, which conducts the mucus to the 

 skin, cannot also convey the air to the intestine. There 

 is consequently a mucus-vessel and an air-vessel, or a 

 Avater- and an air-vessel, an indifferent and a different. 



1936. The mucus-vessel is called absorbent, the air- 

 vessel respiratory duct or trachea. 



1937. Air- and absorbent vessel stand in antagonism 

 like skin and intestine, like water and air. The air- 

 vessel is the skin or the branchia, which passes to the 

 intestine, the absorbent vessel is the intestine, which 

 passes to the air; the one the intestinal branchia, the 

 other the branchial intestine. 



1938. So long as intestine and skin were one in kind, 

 this vascular process was in every situation. With their 

 separation therefore the vascular structure has of neces- 

 sity originated between two opposed situations. There 



