History of a transient nervous apparatus in certain Ichthyopsida. 325 



"Elasmobranch Fishes" *)? where in tab. 12, fig. 1 two of them are 

 shown lying at the dorsal region of the spinal cord. In the descrip- 

 tion of the plate they are spoken as "peculiar large cells which are 

 found at the dorsal part of the spinal cord". They are not noticed 

 in the text. 



In 1884 Victor Rohon ^) published observations "Zur Histo- 

 genèse des Rückenmarks der Forelle". This paper would undoubtedly 

 have attracted greater attention, had it appeared in a more accessible 

 journal than the "Müuchener Sitzungsberichte". It treats of large 

 nerve-cells in the cord which appear earliest of all the ganglion-cells. 

 Their position, i. e. at the dorsal region of the spinal cord of the 

 trout, is correctly described, and they are stated to be multipolar. 

 From them "Zellfortsätze", four or five in number, could be followed 

 for some distance, but what became of these was not made out. The 

 cells are said to make their appearance at the éO^^ day. It was 

 noted that they resemble in appearance the cells of the spinal ganglia; 

 On p. 44 their distribution is correctly given, and their occurrence 

 in pairs, one on each side of the middle line, is recorded. "Man 

 könnte also an eine bilaterale, symmetrische Anordnung derselben im 

 Rückenmark denken — doch ist dies keineswegs der Fall" as is 

 proved by longitudinal sections, where they are seen to be disposed 

 irregularly. None the less "es lässt sich mit aller Bestimmtheit be- 

 haupten, dass jeder Rückenmarkshälfte bloss eine einzige Längsreihe 

 solcher Nervenzellen zukommt". The crossing of a fibre to the oppo- 

 site side, as well as an anastomosis between a right and a left 

 ganglion-cell, is described. Rohon considered that the cells corre- 

 sponded to the large ganlion-cells of Amphioxus described by Stieda ^), 

 as also to Reissner's cells in Fetromyzon. He determined that from 

 6—8 pairs of such cells occurred in the region of each myomere of 

 the trout. The cells are figured as seen in transverse, horizontal and 

 longitudinal sections. Of their subsequent fate nothing is stated. 

 From the figures and text it is obvious to me that in the stages 

 studied by Rohon the cells were in process of degeneration. 



In 1885 in a memoir on the unpaired fins of Elasmobranchii 

 Paul Mater*) devoted about a page to the description of "Riesen- 



1) No. 1 in the List of literature. 



2) No. 13. 



3) No. 14. 



4) No. 10. 



22* 



