30 



NERVOUS SYSTEM AND SENSE ORGANS 



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 Ccrcl>iafnliif< and 

 an anastomosis between the branches of multipolar ganglion cells. 



The nemertineans are divided into groups 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 belo^^■ 

 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 muscle layers. 



4^yL. 4J^ 



Fip. 13. Nervous system anh sense okcans oi' Nemertinea. A. Nervous 

 system of Cerebratidii'^ showinf; chief nerves and the position of the 

 centi-al fibrous mass, Hubrecht. B. Section of e.ve of Drei)a>i()i>h()ri(it. 

 Hubrecht. C. Diagram of head end of Cerebratuhif!. I). Section of 

 eye of Linens, Punnett. E. Brain of Drapannplioru.s, Hubrecht. F. 

 Br) in of Euj)oUa, showinj; fibrou.s core on the right, Hubrecht. G, H. 

 Cross .sections throuRh brain of Enpolia, left side and oesophagus 

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

 lateral cord and ventral Ranglion in A»opla, and DrepanophoniK, 

 Burger. 



Hubrecht, '87, suggests that the more ijrimitive nervous syste''n 

 of these animals has a mo.st complicated intricate network of peri- 



