IX. ON THE SPINAL NERVES OF AMPHIOXUS'. 



DURING a short visit to Naples in January last, I was enabled, 

 through the kindness of Dr Dohrn, to make some observations 

 on the spinal nerves of Amphioxus. These were commenced 

 solely with the view of confirming the statements of Stieda on 

 the anatomy of the spinal nerves, which, if correct, appeared to 

 me to be of interest in connection with the observations I had 

 made that, in Elasmobranchs, the anterior and posterior roots 

 arise alternately and not in the same vertical plane. I have 

 been led to conclusions on many points entirely opposed to those 

 of Stieda, but, before recording these, I shall proceed briefly to 

 state his results, and to examine how far they have been cor- 

 roborated by subsequent observers. 



Stieda 2 , from an examination of sections and isolated spinal 

 cords, has been led to the conclusion that, in Amphioxus, the 

 nerves of the opposite sides arise alternately, except in the most 

 anterior part of the body, where they arise opposite each other. 

 He also states . that the nerves of the same side issue alter- 

 nately from the dorsal and ventral corners- of the spinal cord. 

 He regards two of these roots (dorsal and ventral) on the same 

 side as together equivalent to a single spinal nerve of higher 

 vertebrates formed by the coalescence of a dorsal and ventral 

 root. 



Langerhans 3 apparently agrees with Stieda as to the facts 

 about the alternation of dorsal and ventral roots, but differs 



1 From the Jotirnal of Anatomy and Physiology, Vol. X. 1876. 

 - Mem. Acad. Petersbourg, Vol. XIX. 

 3 Archiv f. mikr. Anatomie, Vol. xn. 



