STOMODAEUM AND MEDULLARY TUBE 



in Vertebrates the first rudiment of the kidney arises as a 



number of separate, segmentally arranged, tubules which 

 show a remarkable resemblance to the so-called segmental 

 organs of Annelids. The agreement of Vertebrates and An- 

 nelids in the excretory system and its rela:ion to the genital 

 products and the segmented coelome has always remained 

 one of the strongest arguments in favour of the Annelidan 

 theory. In recent times the discovery of BOVERl (1890) and 

 Goodrich (1902) that also the closed protonephridia of 

 parenchymatous worms, Rotifers and several Annelids, are 



Fig. 1. A. Segmental organ of the Polychaet Phyllodoce. 

 o. external aperture, 

 s. solenocyts. 

 B. One of the terminal branches. 

 A' Segmental organ of Amphioxus. 

 B^ One of the terminal branches. 



From Boas (1914), after GcoZRiCH. 



-found again among Chordates in Amphioxus has lent a 

 valuable support to this theory. The solenocytes, a veiy 

 specialized form of flame-cells, are found only in Amphicxus 

 .and certain Polychaets ; their structure and arrangement in 



