KUTCHIN. — PERIPHERAL NERVOUS SYSTEM OF AMPHIOXUS. 577 



the ventral border of the rostrum. According to his figures this nerve 

 (III) makes its exit near the root of nerve II. In a few cases (ilhis- 

 trated by his Fig. 9) Dogiel observed directly posterior to the large 

 root of nerve II two small nerves, which he designated as nerves III 

 and IV. Neither of these possesses a ventral ramus which reaches to 

 the ventral border of the rostrum; in such cases the skin of the rostrum 

 is in part supplied by his nerve V. It is clear from his figure that the 

 nerve numbered V is the one usually designated as III. 



From the foregoing description it will be seen that Dogiel does not 

 regard the anterior sensory nerves as occupying definite relations to 

 the myomeres. Changes in the numbering of the anterior sensory 

 nerves must of course affect the numbering of all the other sensory 

 nerves. Thus one, two or three roots in the region of the exit of nerve 

 II, if designated in accordance with Dogiel's view as separate nerves, 

 would correspondingly change the numbering of all the succeeding 

 dorsal nerves, which show such a constant relation to the muscle seg- 

 ments. Since the two sides are frequently not symmetrical with 

 regard to the number of roots in the region of nerve II, one might have, 

 according to Dogiel's system of enumeration, the correspondingly 

 numbered nerves of the two sides belonging to myomeres 7iof cor- 

 respondingly numbered. 



I have examined a large number of specimens, frequently with the 

 aid of artificial light, and find that roots accessory to the main root 

 of nerve II are often present, as is shown in my Figures U and 12 

 (PI. 3). These two figures present the two sides of the same indi\'idual 

 and illustrate the manner of exit of the roots of nerves II and III, and 

 their relation to the myomeres. They also show the lack of symmetry 

 in the roots of nerve II on the two sides of the body. Figures 6 and 7 

 (PI. 2) show other conditions in the roots of nerve II. These do not 

 differ in their form and position from the nerves described by Dogiel 

 for this region. The main root of nerve II, and those roots that make 

 their exit in close proximity to it, always lie anterior to the first myo- 

 mere of the adult. Small roots may lie considerably posterior to the 

 main root of nerve II and still occupy a position anterior to the first 

 myomere. This is possible owing to the form of the muscle segment. 

 Examination of a large number of individuals leaves in my mind no 

 doubt of this condition. A distinct myomere intervenes between the 

 root (or roots) of nerve II and that of the commonly accepted nerve 

 III (Figs. 11 and 12). Moreover, the territories innervated by these 

 nerves, while subject to some variation, are comparatively well 

 defined. The dorsal nerves make their exit in definite relation to the 



