5i8 J. PERCY MOORE. [Vol. X. 



representing three pairs of coalesced ganglia which succes- 

 sively diminish in size toward the posterior end (Fig. i). The 

 anterior eight are situated in the major annuli of the corres- 

 ponding number of somites. They are of equal size and simi- 

 lar form ; the posterior lobe of each being slightly smaller than 

 the anterior. The fifth and sixth are slightly displaced to the 

 right of the middle line, respectively by the spermatheca and 

 the atrium, especially the sixth, which is also turned on edge 

 and bound to the muscular wall of the copulatory bursa. 

 Dorsally all of these ganglia rise above the level of the nerve 

 cord (Figs. 7,11, and 18) to which they are broadly attached ; 

 forming a series of grooves in which the supra-neural vessel is 

 accommodated. Three pairs of nerves spring from the region 

 of each pair of ganglia, one from each end and one from the 

 transverse constriction (Fig. 18). These supply the body 

 walls, and are readily traced between the two layers of mus- 

 cles, splitting up as they proceed. The first and second nerves 

 supply the major annulus alone, the third (posterior) divides, 

 one branch passing to the major, the other to the minor annu- 

 lus. The posterior mass is related to the caudal concentra- 

 tion of somites for the support of the sucker, and lies posterior 

 to the septum 8-9. It does not differ in minute structure from 

 those anterior. The anterior ganglion of the mass is larger 

 and the posterior smaller than the isolated pairs of ganglia. 

 Several lateral nerves have their origin here, and the cord ter- 

 minates in a brush of smaller nerves which supply the numer- 

 ous glands and muscles of the region. Long narrow fissures 

 appear along the middle line of the nerve cord at intervals for 

 its entire length, and frequently penetrate completely through, 

 separating the two halves of the cord. 



A thin sheath which encloses the nerve cord for its entire 

 length and includes the supra-neural vessel, appears to be 

 muscular. 



Besides the smaller ganglion cells which make up the bulk 

 of all of the ganglia, each ganglion possesses a small basal 

 group of larger ones (Fig. 18). No visceral nervous system 

 has been detected ; nor any of the large isolated ganglion cells 

 figured by Voigt in connection with the acetabular glands. 



