Miscellaneous. 481 



developed ventral brauehes, corresponding to those of the I'rhtom'ulcn, 

 and it appeared to us that there was a descending branch runtiiiig 

 along the pharynx, and appearing to unite with its homologue on 

 the opposite side : this nerve would perhaps represent the latero- 

 dorsal nerve of the Tristomidce. 



The two internal and external ventral nerves of each side (the 

 internal one being stronger and following the contour of the repro- 

 ductive organs, the external more slender and more incurved) start 

 from the infero-posterior extremity of the brain and unite in the 

 posterior region of the body, a little in advance of the sucker, form- 

 ing a little ganglion on each side, which gives off a nervous branch. 

 ^Ye did not determine the presence of commissures between the 

 right and left nerves, but those of the same side are united by three 

 transverse branches, and the internal nerve sends off a few rami 

 which pass to the neighbouring organs. 



The nervous system of Microhotlinum apiculatum is the most 

 complicated yet observed ia the group. Besides the brain, there 

 exist two post-pharyngeal centres united by a transverse commissure, 

 and a large ganglion in the posterior region of the body. The 

 brain, which is much reduced in size, gives off anteriorly only two 

 branches, which correspond to the first pair of nerves in the 

 Tristomidce. Posteriorly, it is prolonged on each side of the pharynx 

 into a branch passing to the pharyngeal ganglion, and giving off two 

 little threads, which are perhaps homologous to the second and 

 third pairs of Pseudocotifle. The pharyngeal ganglia are two large 

 nervous masses united by a transverse branch ; from the latter 

 there arises a pair of verj' short nerves, corresponding to the latero- 

 dorsal nerves of the Tristomidce ; from each ganglion there are given 

 ofi' two longitudinal nerves (internal and external ventral nerves) 

 and two accessory ones which lose themselves in the parenchyma ; 

 lastly, from the extremity of the ganglion there arises an anterior 

 nerve, which seems to prolong the external ventral nerve, and 

 extends as far as the mouth, uniting in its course with the branch 

 passing from the brain to the pharyngeal ganglion : this nerve 

 appears to represent the third anterior pair of the Tristomidce. The 

 two ventral nerves are united to one another by three commissures 

 as in Pseudocotyle. Posteriorly they enter a ganglion whence four 

 pairs of nerves are given off, of which three are posterior and one 

 tolerably long anterior ; this important nervous apparatus corre- 

 sponds to the power of the muscular system in this region. 



These researches show, on the whole, that the nervous system of 

 the Monocotylidce is constructed on the same plan as that of the 

 Tristomidce^ but exhibits a somewhat greater degree of complication, 

 which we should not have expected. — Comjptes Itendus, tome cxiii. 

 no. 4 (July 27, IS'Jl), pp. 225-227. 



