38 BRISTOL. [VOL. I. 



The anal ganglia comprise ten neuromeres; the three ante- 

 rior neuromeres differing but slightly from normal body neuro- 

 meres, while the succeeding seven are modified by condensation. 

 These latter represent the seven neuromeres in the anal ganglia 

 of Clepsine, while the former mark the extent to which fusion 

 has gone on in Nephelis beyond that in Clepsine. In the 

 former the nerves emerge in two pairs with the " Leydig's cells" 

 between them; in the latter they emerge fused into a single 

 trunk with the " Leydig's cell " lying alongside. The distribu- 

 tion shows the limits of the metameres as given above. 



In the anterior end of the nerve chain, the "brain*' and 

 suboesophageal ganglia, though much more modified, yield to 

 the plan of the body neuromere, and again the distribution 

 readily defines the limits of the metameres. The suboesophag- 

 eal ganglia consist of five neuromeres. II lies on the side of 

 the collar, while III to VI are closely fused together, yet each 

 neuromere of this region contains every factor that goes to 

 make up a body neuromere. 



The nerves of the last neuromere, VI, emerge as in a body 

 neuromere, the others as single trunks. In neuromere VI the 

 "Leydig's cell" lies between the nerves; in V it lies in the 

 angle of the first branching; in the others it lies alongside 

 the trunks.' 



The "brain" or neuromere I lies above the oesophagus. In 

 it, as in the other neuromeres, is found every unit that is 

 found in a body neuromere. The "brain," therefore, does not 

 differ morphologically from any other neuromere. The distri- 

 bution in this fused region shows on analysis the same mor- 

 phological arrangement as in the body metamere, and the 

 division of this region into metameres as given above was 

 derived from this source. 



The Intermuscular Nerve Ring. In the second and fifth 

 annuli of each body metamere, between the layers of the longi- 

 tudinal muscles and the circular muscles, are found two rings of 

 nerve cells and fibers. Each ring receives fibers from the cen- 

 tral system and from sensillae on the surface, and gives rise to 

 fibers that go to the central system and to the muscles. At 

 definite and constant points about the ring are ten groups of 



