132 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



The occurrence of a continuous rod or fibre in such a position was so 

 surprising, and the sharpness and detiniteness of its appearance so con- 

 vincing, that I was unable to accept the views of previous observers as 

 to its nature. I immediately devoted my time to its investigation and 

 soon succeeded in proving that " the fibre is an organic structure, occur- 

 ring in all classes of vertebrates, and intimately connected with the 

 central nervous system which surrounds it, but within the lumen of 

 which it lies for the most part free " (Sargent, :00). 



Further studies on its development and cellular connections led to 

 the discovery of a highly specialized apparatus, of which the so-called 

 Reissner's fibre forms the conduction path, fur the transmission of motor 

 reflexes (Sargent, :01, :01^). 



More extended research has shown this apparatus to be one of the 

 most archaic structures of the central nervous system, and has enabled 

 me to trace its phylogenetic development throughout the sub-phylum 

 Vertebrata, within which it reveals many minor changes in structure 

 and some modifications of function. 



It gives me pleasure to acknowledge my indebtedness to Prof. E. L. 

 Mark for his able supervision and criticism of the work while in progress, 

 and for his painstaking revision of the manuscript. I am also indebtcfd 

 to Prof. (I. II. Parker for a number of criticisms and suggestions, and 

 to Dr. II. C. Burapus, formerly Scientific Director of the Wood's Hole 

 Laboratory of the United States Fisli Commission, who extended to me, 

 while an occupant of one of the Tables controlled by the Museum of 

 Comparative Zoology, opportunities for collecting a large amount of the 

 material on which these studies are based. I desire to express my thanks 

 likewise to Dr. II. M. Smith, the Scientific Director of the United States 

 Fish Commission, for similar courtesies. I also acknowledge obligations 

 to Prof. Burt Wilder, Prof. C. H. Eigenmaun, and the late Dr. N. K. 

 Harrington for valuable material which I could not have secured but for 

 their aid. 



I. Morphological. 



A. General Historical Survey. 



1. Reissner's Filn'e. 



It is remarkable that so peculiar and conspicuous a structure as 

 Reissner's fibre, which is of so great importance in the nervous anatomy 

 as to persist throughout the vertebrate series, should have remained for 

 forty years after its discovery so little known. This is, no doubt, largely 



