159 
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 relation 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 BOVERI (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. 
0. extern erture. 
s 
B. One of the terminal branches. 
A! Segmental organ of Amphioxus. 
B! One of the terminal branches. 
From Boas (1914), after GOODRICH. 
found again among Chordates in Amphioxus has lent a 
valuable support to this theory. The solenocytes, a very 
specialized form of flame-cells, are found only in Amphioxus 
and certain Polychaets; their structure and arrangement in 
