50 



NKRNOUS SYSTEM AM) SENSK ()R(]ANS 



lateral cords they increase in number posteriorly and are more 

 abundant on the dorsal side. In each lateral cord both dorsally and 

 ventrally are radial clusters of medium sized cells showing a bi- 

 lateral arrangement. 



Haller. 1889, shows a neuroglia network in Ceiehratiilns and 

 an anastomosis between the branches of multipolar ganglion cells. 



The nemertineans are divided into groilps somewhat by the 

 position of the nervous system in relation to the body-wall. The 

 more primitive condition seems to be when the brain and chief 

 branches are outside the muscle layers, in the epithelium or below 

 the basement membrane. In some the nervous system is found 

 in the muscle layers of the body-wall and in others the brain and 

 chief nerves lie in the parenchyma internal to the mu.scle layers. 



Nervous system an'h sense okuans of Nemeutinea. A. Nervou."! 

 system of Cerebral ulii.i showing chief nerves and the position of the 

 cential fibrous mass, Hubrecht. B. Set'tion of eye of Drcpanophoriis. 

 Hubreeht. C. Diapram of head end of Cerebratiiliis. D. Section of 

 eye of Linens, Pitmiett. E. Brain of DrapaiioplwrH.i, Hubrecht. V. 

 Briin of Riqitilia. showing fibrous core on the risht. Hubrecht. G. H. 

 Cross sections through brain of RitpoUa, left side and oesophajrus 

 shown in each. I, J. Scheme of some nerve cells and fibers in the 

 lateral cord and ventral panplion in Annpla, and Drepanophoms. 

 Biirjrer. 



Hul)recht, '87, suggests that the more primitive nervous system 

 of these animals has a most complicated intricate network of peri- 



