STUDIES OX THE ECTOPAllASITIC TIIEMATODES OF JAPAN. J J 



interval« by nuiueroiis coiiiiiiissure.s, which all lie in the .same .straight 

 line (PI. XXI, fig. 1). At a short distance from the brain, a branch 

 is given oiï from the internal lateral nerve towards the median line ; 

 this cnrves inwards and supplies the pharynx. Besides the regular 

 commissural nerves Lang'-' has described others M'hich take more 

 or less irregular courses. I have observed similar nerves ; but 

 they seem to be of (juite irregular occurrence, and to run in various 

 directions, Ijut more or less parallel to the diagonals of the rectangles 

 formed by the lateral nerves and their commissures. I have re- 

 presented such a nerve in the anterior part of the body in fig. 1, PI. 

 XX. Again, in Tristomum in the posterior part of the body, just 

 before the suckers, the commissures of tlie two internal lateral nerves 

 give off In'anches which anastomose variously with one another as 

 well as with the neighbouring commissures, and form a network in 

 this region (PI. XX, fig. 1). The commissural nerves are con- 

 tinued towards the lateral parts of the body and there divide into 

 numerous branches. In the posterior part of the body there are, 

 besides the direct continuations of the commissural nerves, others 

 which branch off" from these and proceed towards the lateral part of 

 the body ; so that the transverse nerves in the lateral parts are more 

 numenuis than the regular commissures. 



lu Axiue (PI. A'll, fig. 1), the internal lateral nerve of one side is 

 much lono'er than its fellow of the <3ther side, and ü'ives off a large 

 nerve at about the middle of the seemingly posterior border of the 

 body, which then proceeds along it close to the suckers in a dia- 

 metrically opposite direction from the main nerve. This branch is to 

 be regarded as a special development of one of the commissural nerves 

 which are no doubt present in this genus also. The nervous system also 



1). Lang — Untersuch, z. vei'gleich. Anatomien. Histologie des Nervensystems der Plathel- 

 minthen. IE. Mitheil. a. d. zoolog. Station zu Neapel, Bd. 2, 1881. p. 35. 



