404 



Dr. O. Burger on the 



Carinina. 

 Oarinella. 



Carinovia. Cephalothrix. 



Enopla. 



Group II. 



Tlie central nervous system is dlvifled into a brain and 

 lateral cords. In addition to the swollen anterior portion of 

 the lateral cords, which forms the ventral ganglia, the brain 

 always shows traces of a pair of dorsal ganglia, which, in the 

 highest forms, far exceed the ventral ganglia in size, while 

 the degree to which they are developed appears to depend to 

 a certain extent on the development of the lateral organs. 

 This is proved by the most primitive forms, in which both 

 lateral organs and dorsal ganglia are of simple structure and 

 small size. In the higher forms, however, in which the 

 lateral pits are reduced in size, as we have found to be the 

 case in Prosadenoporus^ the dorsal ganglia by no means 

 undergo a corresponding reduction. The ganglia of the 

 brain are nnited by a dorsal commissure, which passes above 

 the rhynchodajum in CarineUa and above the rhynchocoelom 

 in CcrehratuJus and Drepanophorus. A ventral commissure 

 passes below the rhynchocoelom and in the Enopla lies upon 

 the fore-gut. The position of the brain is consequently by 

 no means absolutely constant even in this respect. Many 

 Nemertines have been shown to possess an anal commissure 

 connecting the two nerve-cords. The central nervous system 

 possesses a variously constituted sheath of ganglion-cells, 

 which differ exceedingly in form, according to the particular 

 region of the brain, and are eminently characteristic of the 

 various regions. The brain and lateral nerve-cords of certain 

 representatives of Group II. {Cerehi-atuhs and Langia) 

 possess neurochord-cells and branched neurochords, wliich 

 traverse the central substance of the lateral cords. Represen- 

 tatives of Grou}) 111. [Drej^anoplwrus and Prosadenojwrus) 



