THE SPINAL NERVES OF AMPHIOXUS. 



two sides, as was first stated by Owsjannikow, and subsequently 

 by Stieda and Langerhans ; but to my surprise not a trace 

 could be seen of a difference of level in the origin of the nerves 

 of the same side. 



The more carefully the specimens were examined from all 

 points of view, the more certainly was the conclusion forced 

 upon me, that nerves issuing from the ventral corner of the 

 spinal cord, as described by Stieda, had no existence. 



Not satisfied by this examination, I also tested the point by 

 means of sections. I carefully made transverse sections of a 

 successfully hardened Amphioxus, through the whole length of 

 the body. There was no difficulty in seeing the dorsal roots in 

 every third section or so, but not a trace of a ventral root was to 

 be seen. There can, I think, be no doubt, that, had ventral 

 roots been present, they must, in some cases at least, have been 

 visible in my sections. 



In dealing with questions of this kind it is no doubt difficult 

 to prove a negative; but, since the two methods of investiga- 

 tion employed by me both lead to the same result, I am able to 

 state with considerable confidence that my observations lend no 

 support to the view that the alternate spinal nerves of Amphi- 

 oxus have their roots attached to the ventral corner of the 

 spinal cord. 



How a mistake on this point arose it is not easy to say. 

 All who have worked with Amphioxus must be aware how diffi- 

 cult it is to conserve the animal in a satisfactory state for 

 making sections. The spinal cord, especially, is apt to be 

 distorted in shape, and one of its ventral corners is frequently 

 produced into a horn-like projection terminating in close con- 

 tact with the sheath. In such cases the connective tissue 

 fibres of the sheath frequently present the appearance of a 

 nerve-like prolongation of the cord ; and for such they might 

 be mistaken if the sections were examined in a superficial 

 manner. It is not, however, easy to believe that, with well 

 conserved specimens, a mistake could be made on this point 

 by so careful and able an investigator as Stieda, especially 

 considering that the histological structure of the spinal nerves 

 is very different from that of the fibrous prolongations of the 

 sheath of the spinal cord. 



