34^ Journal of Comparative Neurology, 



ullated sympathetic fibers contribute to the formation of the 

 distal excess, and therefore if these fibers were added more 

 rapidly in the older than in the younger nerves, then the distal 

 excess w^ould be higher for the larger specimens. Table II does 

 not show this to be the case. Indeed if it can be assumed, as 

 is probably the case, that the sympathetic fibers in question 

 acquire their medullary sheaths after they have grown into the 

 nerve trunk, then they would be counted in both sections of 

 the trunk and would not enter at all as a factor giving rise to a 

 greater number of fibers in the one section than in the other. 



These medullated sympathetic fibers would, however, 

 affect the percentage values of whatever number of fibers there 

 may be growing into the nerve trunk from the spinal ganglion 

 or ventral root and which have not yet reached the locahty of 

 the more distal section of the trunk. They would decrease the 

 percentage values by simply increasing the total number upon 

 which the percentage is based. The table shows that as the ani- 

 mal advances in weight the rate of growth for the trunk de- 

 creases more rapidly than that for either root. 



Therefore the principal conclusions to be drawn from Table 

 III are (i) the younger or more rapidly growing specimen 

 acquires nerve fibers more rapidly than the older ones ; (2) as a 

 whole the rate of growth for the dorsal root is greater than that 

 for the ventral root ; and (3) the rate of growth tends to be 

 higher for the trunk or distal side of the spinal ganglion than 

 for the central side, showing that the growth of the trunk can- 

 not depend wholly upon the growth of the two roots. 



Another interesting set of growth relations is suggested in 

 Table III but can be best brought out in a separate table. 



VIII. The Relation Between the Weight of the Frog 

 AND THE Number of Fibers Contained in its Spinal 



Nerves. 



That the larger frog possesses the larger spinal nerves is 

 a matter of simple observation. The relations, however, be- 

 tween the gain in weight and the increase in the size of the 

 nerve were first investigated, for the frog at least, by Birge ('82). 



