EXISTENCE BETWEEN BODY-CAVITY AND VASCULAR SYSTEM. 25 



system. This opens on the one hand into the body-cavity by 

 means of open stomata, and on the other by means of the thoracic 

 duct into the venous system. 



That fluids can pass from the body-cavity into the blood system 

 by means of the lymphatic system has been shewn both by 

 Recklingshausen and by Ludwig. The former found that milk 

 put upon the peritoneal surface of the central tendon of the 

 diaphragm — where numerous stomata exist — shewed little eddies 

 caused by the milk globules passing through the stomata and 

 entering the lymphatics. Ludwig's experiment is even more conclu- 

 sive. He took a dead rabbit, and removed its viscera, and placed it so 

 that the peritoneal surface of the diaphragm was exposed. He then 

 poured into this a solution of Prussian blue, and, after imitating 

 the respiratory movements for a few minutes, he obtained the lym- 

 phatics filled with a blue injection, shewing a beautiful plexus. 



A more direct communication between the blood system and 

 part of the body-cavity has been described in one Vertebrate. 

 Weldon' has described and figured the structure of the head 

 kidney in Bdellostoma Forsteri. He finds running through the 

 substance of this organ a number of fine tubules, lined with 

 columnar cells and anastomosing with one another. These tubules 

 open on the one hand into the pericardium and on the other into 

 a central duct. In this duct lies a clot which is exactly similar 

 to the blood clots found in the surrounding blood vessels. Further, 

 in some cases capillaries were seen to enter this duct. There 

 seems to be no reason to doubt that in this animal we have a part 

 of the vascular system in communication with a part of the body- 

 cavity through the tubules of the head kidney. 



That there is a very primitive connection between these 

 systems, is further supported by the remarkable observations of 

 Seeliger\ and Van Beneden and Julin* in the development of the 

 heart of Clavellina. 



1 " On the Head Kidney of Bdellostoma," by W. F. E. Weldon. Q. J. M. S. 



Vol. 24, 1884. 



2 "Die Entwicklungsgesohiohte der Sooialen Ascidien," Oswald Seeliger. 

 JenaUche Zeitsch. fiir Naturwissemchaft, 1885. 



s "Eecherclies sur la Morphologie des Tunioiers," Van Beneden and Julin. 

 Gand, 1886. 



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