20 



ART. 4. — EKTTAKO NOMÜIiA : 



/ 



■2g 



to the body wall, they proceed downwards 

 and unite with the snbpharyngeal ganglion 

 at its anterior corners. 



The snbpharyngeal ganglion lies under 

 the pharynx in segment II. The ventral 

 ganglia are large, occupying nearly the whole 

 length of the segments, and give off certain 

 pairs of nerves to the body wall and the 

 visceral organs. In the ventral nerve cord 

 are found three longitudinal canals, one 

 median and two lateral. 



The median canal commences mostly in 

 segment V, but in younger specimens it 

 sometimes begins more posteriorly. In the 

 anterior part of the body the canal is more 

 spacious than in the posterior, and it is 

 always situated at the dorsal median line of 

 the nerve cord. The lateral canals com- 

 mence in segment II ; they are at first in- 

 constant in position, but in segment IV they 

 lie close to the dorsal border of the cord ; 

 and from segment V backwards they are 

 either united or lie side by side with the 

 median canal. These lateral canals are small 

 in the anterior segments, but always larger 

 than the median canal in the posterior segments. In the seg- 

 ments near the end of the body none of these canals are present. 

 They contain a slightly staining substance and are bounded by 

 nerve and muscle fibres. 



The brain apparently consists of two layers : an outer layer 

 consisting of ganglion cells with dense cytoplasm and an inner 

 surrounded by the former dorsally and laterally. The inner layer 

 is entirely made up of nerve fibrils which run in all directions 

 and intermingle with one another. These two layers are present 

 in all the other ganglia ; but their relative positions are reversed 

 in the ventral nerve cord, the cellular layer lying here on the 



Fig. 9. 

 L. gotoi. Brain and an- 

 terior portion of ventral 

 nerve cord ; reconstructed. 

 xl30. ap — Literal prosto- 

 mial nerve, prg — prosto- 

 mial ganglion, br— brain, 

 vn — peripharyngeal com- 

 missure, nc — ventral nerve 

 cord, lg — first ventral or 

 subpharyngeal ganglion, 

 2g— second ventral gang- 

 lion. 



