TECHNICAL NOTES AND BIBLIOGRAPHY 239 



testable point is that the early vertebrates won the 

 fresh-water habitat because they were waterproofed. 



Berrill {28} sees in Amphioxus a degenerate form of 

 the pre-Cambrian larval tunicates, which unhke the pro- 

 tovertebrate, returned to the sea and lost its head. He 

 considers it in no way ancestral to the vertebrates 'and 

 not even a satisfactory vertebrate type.' 



In arguing against the eurypterid theory the vmter 

 has drawn on Schuchert and Dunbar {17, p. 193}, and 

 Gregory {33, p. 62 f}. The eurypterids illustrated in 

 Figure 4 are redrawn from Schuchert and Dunbar. 



In 1946 White {48} described an ostracoderm from 

 the late Silurian of Lanarkshire, which he named Jamoy- 

 tius kerwoodi. The two known specimens show no trace 

 of either endoskeleton or exoskeleton, although the seg- 

 mental muscles are remarkably well preserved. Jamot/tius 

 had long horizontal fin folds, a long, spineless, dorsal fin, 

 and a short anal fin. White considers that it comes close 

 to the ideal 'chordate' ancestor, which he beUeves was 

 an unarmored form. Gregory {33, p. 105}, however, sug- 

 gested that Jamoytius may be intermediate between the 

 anaspid ostracoderms and Amphioxus, and hence, by 

 impHcation, secondarily naked. We would supplement 

 Gregory's interpretation by remarking that a single 

 naked' ostracoderm carries little weight against the large 

 numbers of armored or heavily scaled forms that are now 

 known and it cannot, in the light of the present evidence, 

 controvert the generally accepted thesis that armor is a 

 basic and primitive character of the earhest vertebrates. 



IV. THE KIDNEY 



49. Bridge, T. W. Cambridge Natural History: Fishes. 

 MacmiUan Company, London, 1922. 



50. CusHNY, A. R. The Secretion of the Urine. Long- 

 mans, Green and Company, Ltd., London, first edi- 

 tion, 1917. 



