THE SPINAL NERVES OF AMPIIIOXUS. 697 



In the first place, he states that by isolating the spinal cord 

 by boiling in acetic acid, the anterior roots may be brought into 

 view as numerous conical processes of the spinal cord in each 

 segment. I find by treating the spinal cord in this way, that 

 processes more or less similar, but more irregular than those 

 which he figures, are occasionally present ; but I cannot persuade 

 myself that they are anything but parts of the sheath of the 

 spinal cord which is not completely dissolved by treatment with 

 acetic acid. By treatment with nitric acid no such processes are 

 to be seen, though the whole length and very finest branches of 

 the posterior nerves are preserved. 



By treating with nitric acid and clarifying by oil of cloves, 

 and subsequently removing one half of the body so as to expose 

 the spinal cord /// sitii, the origin and distribution of the posterior 

 nerves is very clearly exhibited. But I have failed to detect 

 any trace of the anterior nerve-roots. Horizontal section, which 

 ought also to bring them clearly into view, failed to shew me 

 anything which I could interpret as such. I agree with Schneider 

 that a process of each muscle-plate is prolonged up to the an- 

 terior border of the spinal cord, but I can find no trace of a con- 

 nection between it and the cord. 



Schneider has represented a transverse section in which the 

 anterior nerves are figured. I am very familiar with an ap- 

 pearance in section such as that represented in his figure, but I 

 satisfied myself when I previously studied the nerves in Amphi- 

 oxus, that the body supposed to be a nerve by Schneider was 

 nothing else than part of the intermuscular septum, and after re- 

 examining my sections I see no reason to alter my view. 



A very satisfactory proof that the ventral nerves do not exist 

 would be found, if it could be established that the dorsal nerves 

 contained both motor and sensory fibres. So far I have not 

 succeeded in proving this ; I have not, however, had fresh 

 specimens to assist me in the investigation. Langerhans 1 , whose 

 careful observations appear to me to have been undervalued by 

 Schneider, figures a branch distributed to the muscles, which 

 passes off from the dorsal roots. Till the inaccuracy of this 

 observation is demonstrated, the balance of evidence appears to 

 me to be opposed to Schneider's view. 



1 Arfhi'' f. Mikrus. Anatowie, Vol. xil. 



B. 45 



