Hardesty, spinal Nerves of the Frog. 325 



the excess is in many cases greater than the entire number of 

 fibers in the ventral root. 



3. The average percentage increase in the number of 

 fibers per miUimeter of length is greater for the dorsal root 

 than for the ventral root. 



4. The average percentage increase of fibers per milli- 

 meter of length tends to be greater for the trunk than it is for 

 either root. 



5. The average rate of growth or increase of fibers per 

 millimeter of length is greater for the smaller specimens than 

 for the larger ones. 



6. In proportion to its weight, the smaller frog has a 

 greater number of fibers in its ventral root, dorsal root, and its 

 nerve trunk. In both the large and the small frog the propor- 

 tions of fibers in the three localities are quite similar. 



7. As the animal increases in weight, for each gram 

 gained in weight, it gains in its 6th. spinal nerves alone, about 

 2.7 ventral root fibers, 4.7 dorsal root fibers and 10.4 fibers in 

 the trunk and dorsal branches. 



Thus it may be seen that the frog gains dorsal root fibers 

 more rapidly than ventral root fibers, and, on the other hand, 

 gains fibers on the distal side of the spinal ganglion, more 

 rapidly than in either root. 



8. There is a general tendency toward a more rapid addi- 

 tion of fibers during the warmer months of the year. That 

 the results are not more decided, may be due either to the fact 

 that the frogs used in winter were not in the normal hibernat- 

 ing condition, or that some ingrowing fibers may not reach 

 their destination during a single season. 



II. Introduction. 



In a previous paper issued from this laboratory,^ counts 

 were made of the fibers contained in the dorsal and ventral 

 roots and in the nerve trunk and dorsal branches of the spinal 

 nerves of the frog. In case of each nerve, counts were made 



Hardesty, I.: Journal of Comparative Neurology, Vol. IX, No. 2, 1899, 



