KUTCHIN. — PERIPHERAL NERVOUS SYSTEM OF AMPHIOXUS. G17 



the transverse muscles are inner\'ated by fibers carried by the dorsal 

 roots. 



He\7nans et van der Stricht ('98) believe that the presence of a 

 pair of dorsal nerves behind the last ventral pair indicates the disap- 

 pearance, or non-appearance, of a posterior myotome, and on this 

 basis regard each dorsal root as corresponding to the following, not 

 the preceding (as Hatschek states), ventral root. The division of a 

 root into dorsal and ventral portions (Retzius) is based on an optical 

 illusion, or on the effect produced by sections. The motor fibers, 

 studied largely on Golgi preparations, penetrate between muscle 

 plates and reach the peripheral zone of the myotome; they sometimes 

 branch. Both ascending and descending fibers show varicosities, 

 consisting of regular and of irregular swellings. The regular swellings 

 are probably nuclei, but those of irregular occurrence are artifacts. 

 Motor fibers shovt' definite terminal bodies, which are flattened and 

 conical, of spatulate form; they are perhaps to be considered as 

 motor plates of the cylindrical muscle fiber, upon which the terminal 

 nerve fiber inserts itself, not perpendicularly, but laterally. From the 

 number of these terminal plates the authors believe that each muscle 

 fiber is innervated. The nerve fibers of the ventral roots are non- 

 medullated, and thicker than those of the dorsal roots. The striated 

 fibers in ventral roots are not nerve fibers, but muscle fibers, deflected 

 from their usual course. 



Dogiel ( : 02) impregnated motor fibers and end-plates with methy- 

 lene blue. He finds that the typical motor nerve ending is not a 

 plate, but a flattened cone, the basal surface of which lies on the 

 surface of a muscle plate. The cones appear larger in Golgi prepara- 

 tions than in those impregnated with methylene-blue, because in the 

 former case silver is deposited to some extent in the muscle as well as 

 in the nerve. Dogiel finds motor fibers penetrating (centripetally) 

 the ventral part of the ner^•e cord in more or less thick bundles. 

 These fibers arch backward, and can be followed for some distance. 

 Certain fibers bend downward under the central canal, either from 

 right to left, or vice A'ersa, and. so constitute a kind of commissural 

 fiber. Dogiel could not follow fibers to cells, but states that they do 

 not divide into fine threads, nor form a net on entering the nerve cord. 

 Although he says that few varicosities are present in methv'lene-blue 

 preparations, his Figures 43, 44a, and 446, show frequent swellings 

 in the motor nerve fibers. Repeated branchings of the motor fibers 

 in their course toward the periphery are seen in his Figure 41. 



In my own study the most successful impregnations of motor fi])ers 



