No. I.] THE METAMERISM OF NEPHEUS. 43 



I believe that I have found the source of these fibers in 

 the bipolar cells that lie in the intermuscular nerve ring, the 

 description of which will be given later. 



Innervation of a Body Metamere. 



As I have said before, the ganglion lies in the first ring of 

 the somite and the two lateral nerves pass out, for a little 

 distance, in a horizontal plane and at right angles to the long 

 axis of the body. Then they divide into dorsal and ventral 

 branches, and again divide and subdivide to innervate the 

 various organs, as described in detail below. The first and 

 most striking fact is that the distribution is morphologically 

 identical with that of Clepsine, and the second that it confirms 

 Professor Whitman's explanation of the derivation of the five- 

 ring metamere from a three-ring type: e.g., Clepsine. 



A glance at PI. V, metamere VIII, will show that the 

 anterior nerve innervates the 4th and sth annuli of the pre- 

 ceding metamere on the ventral side and the extreme lateral 

 sensillae of the ist annulus of its own metamere, and sends 

 fibers to the intermuscular nerve ring in the 5th annulus. 

 The posterior nerve sends one ventral branch to the sense 

 organs on the ventral side of the 3d annulus and two ventral 

 branches to the intermuscular nerve ring in the 2d annulus, 

 one of which by subdivision makes two connections with the 

 nerve ring. The principal branch of the posterior nerve is 

 dorsal, and this branch innervates, first, the few dorsal sensillae 

 on the 4th annulus of the preceding metamere ; second, the 

 dorsal side of the nerve ring in the 5th annulus ; third, the 

 large sensillae in the ist ring of its somite; fourth, the dorsal 

 side of the nerve ring in the 2d annulus ; and fifth, a few 

 dorsal sensillae in the 3d annulus. A comparison now with 

 Professor Whitman's work on Clepsine will show how com- 

 pletely identical the distribution is (Pll. IV and V). The 4th 

 and 5th annuli are morphologically the 3d annulus of Clepsine; 

 they are innervated by ventral portions of the anterior nerve, 

 as in Clepsine. The branch of the anterior nerve in Nephelis 

 that represents the middle nerve in Clepsine innervates exactly 



