Johnston, Nerves of Petrouiyzouts. 603 



CALIBER OF FIBERS IN THE LAMPREY. 



A word should be said regarding the relative thickness of fibers 

 in the peripheral nerves. For this the different figures should be 

 compared and notice taken of the magnification in each. In 

 drawing there is a constant tendency to exaggerate the thickness 

 of the fine fibers and in the case of the finest it becomes physically 

 impossible to represent them except at high magnifications. The 

 thickness of the fibers of the ventral spinal roots has been dwelt 

 upon. The dorsal roots (fig. 31) contain medium (5.2/^), fine 

 (1.5//) and very fine (o.i^ix) fibers. The coarse motor fibers in the 

 muscles are approximately seventy-five times as thick as the 

 finest fibers in the dorsal roots. In the base of the gills and in the 

 walls of the water tube and oesophagus and blood vessels the 



Fig. 29. A ganglion cell at the base of a gill filament. Magnification, 250 diameters. 



terminal fibers are just visible under the Leitz ocular 4 and objec- 

 tive 7. The coarser fibers of the sympathetic trunk are between 

 two and three microns in diameter. 



SUMMARY. 



The chief results of this study are as follows: 



I. The great thickness of the motor fibers and their great 

 increase in thickness before entering the muscles; the existence of 

 two distinct types of motor endings and the increasing complexity 

 of the end plates in the myotomes, branchial muscles, and the 

 muscles of the buccal funnel and the tongue; and the great number 

 of muscle fibers innervated by each motor nerve fiber. Fusari 

 (1901) has pointed out that the end plates in the myotomes are 

 simpler than those in the other muscles and mentions that after 



