Kingsbury, Brain of Nectunis. 169 



The Mauthner cells^ are very large, being fusiform in shape 

 and lying transversely to the long axis of the oblongata. The 

 mesally directed process was not seen to branch and is thought 

 to be continuous with the axis cylinder of the Mauthner fiber. 

 The lateral end divided into several (at least three) processes, 

 which extended toward the entering fibers of the auditory 

 nerve; (see Fig. 18.) These cells resisted the silver impregna- 

 tion, and the exact extent and relations of the dendrites (pro- 

 cesses) could not be observed. 



The intimate relation of the processes with the fibers 

 of the eighth nerve has been observed by Mayser, Gorono- 

 witsch, and Burckhardt. Goronowitsch was inclined to regard 

 the processes as giving rise directly to acustic fibers, — a condi- 

 tion irreconcilable with the views at present held of the rela- 

 tions of sensory nerve fibers. Intimately connected is the 

 question of the relation of other large cells to the eighth nerve. 



The Mauthner fibers have not been followed in Nectunis 

 caudad of the third spinal nerve ; as observed in other forms, 

 however, they gradually become smaller caudad until near the 

 caudal end of the abdomen they become indistinguishable. 

 Stieda ('64) states further, that in Amphibia [Axolotl) they do 

 not preserve their large caliber for such a distance as in fishes. 



There is substantial agreement in the observations of dif- 

 ferent investigators as to the structure of the fibers in fishes 

 and dipnoans. By all they are stated to be fibrillar and to give 

 off twigs (collaterals ?) at intervals. In dipnoans {Protoptenis and 

 Ceratodiis) the fibrillar structure would seem to be particularly 

 well marked. Sanders ('89) speaks of them in Ccratodus as 

 multi-axial with axis-cylinders leaving the common sheath at in- 

 tervals. In Nectunts the fibers appear finely fibrillar, but no 



^There would seem but little doubt of the direct continuity of the Mauth- 

 ner fiber and cell. Mayser, ('43) in his investigation of the brain of the cyprin- 

 oids, discusses both fiber and cell at some length. He states the termination of the 

 fiber in the cell. Goronowitsch ('28) in Acipenser, states the fact, or at least his in- 

 terpretation, in the following clear language: " Nach der Kreuzung verlaufen 

 sie bogenformig zum Unterhorne, wo sie in sehr grossen Nervenzellen enden." 



Furthermore, Burckhardt ('91) found bothcell and fibre in Triton, and fig- 

 ures the former and its connection with the Mauthner fiber. 



