48 BRISTOL. [Vol. XV. 



complete the elements of this neuromere. The capsular ele- 

 ments of neuromere I differ from all the others, in that the 

 whole six are carried on the dorsal part of the collar (PL VI, 

 Figs. II and 13). Excepting the position of the ventral cap- 

 sules, the supra-oesophageal ganglion does not differ from the 

 typical neuromere, and the argument made by Whitman (9) 

 for Clepsine applies with equal force to Nephelis. Not only do 

 these nerve trunks, " Leydig's cells" and capsules, show by 

 their analysis the presence of six, and only six, neuromeres in 

 the head region, but the distribution in the peripheral parts 

 confirms it and sets the limits to the terminal somites in the 

 most conclusive manner. 



The gold chloride stain was peculiarly valuable in this work, 

 and gave me sections with which it was only a question of 

 patience to follow out the well-defined nerve branches to their 

 peripheral parts. The fibers stand out distinct in form and 

 color, not to be confused with any other element in the head. 

 The spherical cysts of a parasitic nematode often furnished 

 excellent data for the perfect superposition of the drawings of 

 a series of sections and made it possible to follow out every 

 fiber represented in my drawings through its subdivisions to 

 the sense organs. 



Beginning, as before, at the nth annulus (PI. V, Fig. 2) 

 I find the distribution from behind forward as follows : the 

 nth annulus contains an intermuscular nerve ring, and 

 receives its innervation from the succeeding neuromere, VII. 

 The posterior trunk nerve of VI sends a ventral branch to the 

 loth annulus and a dorsal branch which innervates dorsal 

 sensillae on the loth and 9th annuli, as well as sending a 

 branch forward to the intermuscular nerve ring of annulus 8. 

 The anterior branch is wholly ventral and lateral, innervat- 

 ing the intermuscular nerve ring in the 8th annulus and a 

 few ventral sensillae. The 9th, loth, and nth annuli, there- 

 fore, make up metamere VI, the innervation of which is 

 strictly comparable to that of a body metamere, being dimeric 

 and triannulate. The most striking departure from the five- 

 ring metamere lies in the absence of the intermuscular nerve 

 ring from annulus 10, morphologically the 2d annulus of the 



