1 68 Journal of Comparative Neurology. 



tween the fifth and seventh nerves, they are quite abundant, 

 forming prominences in the floor of the oblongata, — the 

 fiuclcus centralis of Stieda. 



Maiithncrs Fibers. — (Figs. 9-16, 18.) It is interesting to 

 observe the presence of the Mauthner's fibers in Necturus, add- 

 ing another to the forms in which their occurrence has been 

 noted. They appear to be quite constantly present in Teleosts 

 where they have been studied by Stieda ('68), Fritsch, Mayser 

 ('81), Kolhker ('93), and others. They also occur in Ganoids 

 [Acipmscr, Amia, Polypteriis, CalamoicJitJiys, Scaphyrhjmchops,) 

 and in Dipnoans [Ceratodus, Protoptcnis). On the other hand, 

 according to Kolliker they are absent in five genera of teleosts ^ 

 that have been examined and in the Elasmobranchs. In Am- 

 phibia they seem to be generally present in the larval state, and 

 have further been observed in the adult Triton (Burckhardt '91), 

 DesnwgnatJms (Fish '93) ; I have fcrund them in the adult 

 Necturus, Aviblystoma, and Dieniyctylus. Osborn on the other 

 hand states that they were not found in Cryptobranclius and are 

 not generally present in urodeles ; the last statement would 

 appear erroneous, however, from the enumeration above. 



They are stated to be absent (as Mauthner's fibers) in the 

 adult Salamaiuira maculosa, (Burckhardt, '91). In Necturus 

 they occupy their customary position in the dorsal portion of 

 the ventral columns, on each side of the meson. In this posi- 

 tion they may be traced cephalad to their decussation just 

 caudad of the exit of the seventh and eighth nerves, where 

 they cross somewhat obliquely and turn directly laterad to end 

 in, — it is believed, — large cells. They measure about 35 

 micra in diameter, being, it would seem, somewhat smaller 

 than the corresponding fibers in •' fishes ;" (see Kolliker, '63). 

 No apparent regularity seemed to exist in their relation to 

 each other at the decussation, sometimes the right and some- 

 times the left crossing dorsad of its opposite. 



1 These are Orthagoriscus, Tetrodon, Monnynis, Malaptcrrtms, and Gymnotus ; 

 it is interesting to note that the last three are electric or semi-electric fishes. 

 The relation of the first two genera to Fritsch's theory is interesting. 



