KUTCHIN. — PERIPHERAL NERVOUS SYSTEM OF AMPHIOXUS. 593 



correspond to the branch of nerve V described by Hatschek ('92, 

 Figur 6, N'. S.) as passing to the groove of Hatschek. Heymans et 

 van der Stricht ('98) state that the N. recurrens of Hatschek ends at 

 the velum, and has nothing in common with the branchial plexus. 

 I have never observed a large branch from the buccal nerves reaching 

 the branchial basket. 



D. Nerves of the Brnnehial Region. 



In this group are included the dorsal nerves lying between the 

 velum and the region anterior to the atriopore. The term " branchial " 

 is therefore unsatisfactory in some respects, but is perhaps the one 

 most available for use in a description of the nerves. In B. lanceo- 

 latum this region is supplied by nerves VIII to XL, or XLI, inclusive, 

 while in B. caribaeum it seems probable that nerves XXXVIII and 

 XXXIX innervate the region of the atriopore. This indicates that 

 the difference in the number of myotomes in the two species occurs, 

 in part, in the branchial region. Dogiel (:02) states that in B. 

 lanceolatum nerve XLI I is the most posterior nerve supplying the 

 region of the atriopore. He describes the fine-meshed plexus ramify- 

 ing about this opening, and finds that branches of nerves XXXVIII- 

 XLII may take part in its formation. Variations certainly occur in 

 these nerves, as in the case of other dorsal nerves. 



The nerves of this region impregnate particularly well with methy- 

 lene blue, but require a longer immersion than those of the anterior 

 part of the body, especially in the case of the visceral branches. 

 Strong light was very useful in following the finer ner^•e branches in 

 the thicker portions of the body. Various branches of these dorsal 

 nerves have been repeatedly described; the accounts, which are 

 somewhat fragmentary, wnll be taken up in connection with the 

 description of my personal observations. 



The dorsal nerves of this region differ little from each other in their 

 main characteristics, and in certain respects resemble those of the 

 buccal region. It may be noted that, as seen in Plate 2, Figure 6, 

 the arch formed by each dorsal nerve as it leaves the neural tube 

 gradually increases in height toward the middle region of the body. 

 Here the arch remains practically constant, but toward the posterior 

 region it again diminishes in height, and at the extreme posterior end, 

 as will be noted later, no arch is present. In the anterior portion of 

 the branchial region the place of division of the dorsal nerves into 

 dorsal and ventral rami is usually at, or just before, the exit of each 



