KUTCHIN. — PERIPHERAL NERVOUS SYSTEM OF AMPHIOXUS. 595 



Heymans et van der Stricht ('98) and Dogiel (: 02). These branches 

 ramify over the metapleural fold and ventral wall of the atrium, 

 forming a cutaneous network, the meshes of which are generally 

 elongated longitudinally. Ne^^'e VIII is usually the most anterior 

 nerve sharing in the formation of this plexus. Fusari ('89) describes 

 nerve cells and ganglionic knots in connection with this network. It 

 is of interest to note that these cutaneous abdominal branches may 

 leave the ventral ramus at or near the ventral muscle border, or the 

 ventral ramus may divide much earlier in its course, sending one or 

 more twigs from the branches thus formed to the superficial abdominal 

 region (Figs. 37, 39). In Figure 39 the absence of a ramus cutaneus 

 ventralis in connection with nerve XXXVI is to be noted. 



The remaining two divisions of the ventral ramus are freciuently 

 formed from one main short stem; this may bend toward the interior 

 beneath the ventral border of the trunk muscles, or may penetrate 

 a myoseptum at some distance (the width of one, two or even 

 three myomeres) dorsal to this ventral muscle border. These two 

 branches may, howcAer, leave the ventral ramus independently, 

 instead of by a common stem. On the inner surface of the trunk 

 muscles the short stem mentioned above divides into two main 

 branches. One of these, the ramus visceralis ascendens, ascends 

 over the inner surface of the trunk muscles, while the other, the ramus 

 visceralis descendens, descends to the inner surface of the transverse 

 muscles. X'erves VIII or IX, and the succeeding dorsal nerves of this 

 region usually possess a ramus visceralis descendens, but I was unable 

 to find a ramus visceralis ascendens anterior to that of nerve XII. 

 The most anterior ascending visceral ramus is small, but the suc- 

 ceeding one is larger, showing the characteristic fan-like branching. 

 It is entirely possible that branches pass to the most anterior branchial 

 bars from the descending visceral ramus, or the inner abdominal 

 plexus. In this connection it may be noted that the fan-like branches 

 of the most anterior ascending visceral rami observed, were directed 

 obliquely forward. The diagrammatic sketch. Figure 15a (PI. 4), 

 made from several transverse sections, illustrates a fairly typical form 

 of division of the ventral ramus. This shows a branch of a ventral 

 ramus penetrating a myoseptum the width of one myomere abo\e the 

 ventral muscle border. In these sections, stained with Mallory's 

 differential stain, the connective tissue may be readily discerned on 

 either side of the penetrating branch. Upon its exit on the inner 

 surface of the side muscles, the ascending visceral branch takes a 

 course dorsad over the connective tissue covering of the muscles. 



