268 FISH. [Vol. X. 



cells, in the larvae at least, are oppositipolar, and there is no 

 apparent difference between the central and peripheral fibers 

 with regard to caliber. In one instance (Fig. 37) there is 

 shown a very distinct T- fiber, indicating a connection with an 

 unipolar cell, but as no impregnation occurred in the cell an 

 absolute connection could not be established. 



In the Gasserian ganglion of a larval Petromyzon fFig. 52) 

 a unipolar cell is shown which has one central and two periph- 

 eral fibers. In a larval Desmognathus about two centimeters 

 long there was seen a branch given off from the peripheral 

 fiber near the cell, which entered the myel, passing in a caudal 

 direction, and gave off at least one collateral. While this 

 peripheral branch and its connection could be demonstrated 

 with the utmost clearness shortly after the preparation was 

 made, some three months afterwards enough fading had set in 

 to totally obscure this connection. In those cases where the 

 fiber divided into a cephalic and caudal branch no collaterals 

 were seen to arise from the fiber before this division, and 

 when the fibers remain undivided, they were always seen to 

 pass toward the brain, giving off collaterals occasionally. 



Fiber Tracts. 



In the Desmognathus the fibers of the prosencephalic and 

 diencephalic commissures are chiefly of the amyelinic variety 

 as determined by the Weigert method ; as the fibers did not 

 take the hematoxylin in any instance, while in the succeeding 

 segments they stood out with a bright blue color, it seems 

 reasonable to conclude that the absence of the color was due 

 to the absence of the myelin of the fiber. The study of the 

 amyelinic tracts was based upon Golgi preparations and the 

 course and relations of the fibers in most cases were clearly 

 made out. Under the amyelinic tracts are embraced the pre- 

 commissure, callosum, supracommissure, and Meynert's bundle. 



The precommissure is divisible into two parts, the pars olfac- 

 toria and the pars temporalis, Fig. 6. The former is the 

 larger bundle and the fibers pass toward the olfactory lobes. 

 The fibers of the pars temporalis curve around toward the 



