TECHNICAL NOTES AND BIBLIOGRAPHY 243 



associated with the lower intestine and rectum and de- 

 rived from the coelom, and it is thought that uric acid 

 and possibly other metabolites accumulate in these cells, 

 never to be discharged during the life of the animal 

 {49? P- 54 f}- True excretory organs are developed only 

 in the Cephalochordata: in Amphioxus these take the 

 form of many (about loo) pairs of complex nephridia 

 lying at the sides of the dorsal coelomic canals above 

 the pharynx {49, p. 125 f}. The nephridia of Amphioxus 

 are obviously complicated secretory organs and have no 

 similarity to the glomerular-tubular nephron of the 

 vertebrates. 



Biologists who see in Amphioxus the prototype of the 

 earliest vertebrates pass lightly over the fact that the 

 vertebrate nephron could not by any conceivable stretch 

 of the imagination be derived from Amphioxus's ne- 

 phridial complex, while those who see in Amphioxus 

 either a degenerate, simplified ostracoderm {33, p. 84 f } 

 or the permanent larva of some early vertebrate type 

 {15, p. 20} equally overlook the fact that these nephridia 

 could not by a stretch of the imagination be derived 

 from the vertebrate nephron. Moreover, these excretory 

 organs are of ectodermal rather than mesodermal origin, 

 and all the nephridial elements are confined to the 

 pharynx or head (which by the ardent homologizers is 

 homologized with the gill arches of the vertebrates). 

 Romer {15, p. 27} has said that, 'To make a vertebrate 

 out of an arachnid, the supposed ancestor must have lost 

 almost every characteristic feature he once possessed and 

 reduced himself practically to an amorphous jelly fish 

 before resurrecting himself as a vertebrate.' Considering 

 the definitive nature of the glomerular nephron in all 

 vertebrates (with the obvious exception of the aglomeru- 

 lar marine fishes), these discrepancies in the excretory 

 system (despite all other purported homologies with re- 

 spect to 'branchial baskets,' 'notochords,' and the like) 

 are enough to reduce the Amphioxus theory to a jelly in 



