109 



In the Spinal Cord wo wish io direct attention to two 

 peculiarities only. The first is the giant g-anglion cells 

 that are found in the dorsal fissure. Transverse sections 

 of th(^ cord will demonstrate these quite easily. They 

 have been studied especially hy T. 1^. Johnston,* Sargentt 

 and Dahlgren.+ The lattei' author, who has devoted his 

 attention particularly to the Pleuronectidpe, states that 

 these very peculiar cells are the first ganglion cells to he 

 differentiated in the embryo flat-fish, and that they become 

 an important and permanent apparatus in the adult. In 

 an adult fish they are seen to form a row of very large 

 nerve cells in the median dorsal fissure, and their neurites 

 pass backwards to form an isolated fibre tract on the 

 median side of each dorsal horn. Their exact distribution 

 and function are unknown, but Dahlgren suggests that 

 the neurites pass out with the dorsal roots of the spinal 

 nerves and are connected with the sensory supply of the 

 unpaired fins. Sargent finds in (Uenolahrns that the giant 

 cells are connected with a fibre bundle passing forwards 

 through the cord and medulla, and emerging by the 

 ventral root of the trigeminus nerve. If this be true then 

 the fifth nerve of this fish possesses a neive component not 

 hitherto recognised, and it Avould bo interesting to study 

 the giant cell apparatus from the point of view of the 

 component theory. 



The second peculiarity of the cord is one which it 

 shares with all Teleosts, and that is in the presence of the 

 very interesting rod or fibre within the lumen of the 

 central canal known as Iteissner's fil)re. This libie has 

 been investigated recently by Sargent,§ who finds that it 

 " extends through the whole length of the canalis centi'alis 



: J.iiir. Ci.iiii). Xrincl.. \., p. ■"m"). t Anal. Anz.. xv., ji. -IX-l. 



I Anal. All/.. \iii., [>. 'iSI. 



.::; Aiiat. .\ii/.., xvii.. ]). :i:!, and I'roc Aiiu'iicati Acad. Ails and Sciiiicf, 



xxxvi., No. 'i'), 



