ON DIPLOZOON NIPPONICUM, N. SP. 179 



its dorsal side, the other more on the ventral side, close to the dorsal 

 side of the oesophanfus. These 1 have marked in the figure with a 

 lightei' shade. They unite at the two ends of the brain where the 

 nerves take their rise. The l)rain is traversed by numerous dorso-ven- 

 tral bundles as already inentiiuied. 



From the brani are given off nerves both anteriorly and posteri- 

 orly. One pair (Fig. 2. nai) yn'oceeds anteriorly near the median 

 line embracing the pharynx, near the nnterior ])art of which it is lost 

 in the mesenchyma. A second p;nr (nnc) ]^r(U'eeds more laterally, and 

 can be followed as far as the suckers, externally to which it proceeds 

 and there withdraws itself from view. These internal and external 

 anterior nerves are connected with each other by a commissure at a 

 little distance from their origin in the brain. 



Two pairs of nerves also proceed posteriorly, one of which may 

 be called the ventral pair and is by far the stronger ]iair. The other 

 pair (nvl) may be called tiie ventro-lateral nerves and proceeds 

 ])osteriorly just at the angle between the ventral and lateral borders of 

 the body, and can be followed as far as where the two individuals cr(~>ss 

 each other. The ventral nerves (nv) take their rise in the brain at its 

 ])ostero-lateral corner, and ran be followed to near the posterior bor- 

 der of the body, rhey become, liowever, more and more indistinct 

 as tliey proceed ])osteriorly, and finally become invisible at about tlie 

 level of the hinderniost pair of suckers. They closely follow in their 

 course the main excretory vessels, (^n whose ventral side they are 

 situated at a little distance from the muscular layers. At tlie place 

 where the two individuals cross each other and where the ventro- 

 lateral nerves withdraw themselves from view, the ventral nerves take 

 a more lateral position, and this position they keep throughout the 

 remainder of their course. The ventral nerves are connected with 

 each other and with the ventro-lateral nerves by a number of com- 



