THE SPINAL NERVES OF AMPHIOXUS. 2OI 



the first two pairs the nerves of the two sides arise opposite 

 each other ; in the next few pairs, the nerves on the right-hand 

 side gradually shift backwards : the remaining nerves spring 

 alternately from the two sides of the cord. 



For each myotome there is a single nerve, which enters, as 

 in the case of other fishes, the intermuscular septum. This 

 point may easily be determined by means of longitudinal 

 sections, or less easily from an examination of macerated 

 specimens. I agree with Langerhans in denying the existence 

 of ganglia on the roots of the nerves. 



