322 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Plate VII. 



Fig. 52. Plan of the nerve cord of a young specimen 

 about 25 mm. long to show the position of the giant cells. 

 Transverse lines mark the posterior limits of the segment, 

 the numbers of some of which are given at the side. The 

 cells are drawn too large ( x 40) in proportion to the width 

 of the cord ( x 25), and the latter is about twice too broad 

 in proportion to its length ( x 12). The first giant cell is 

 situated in the achsetous segment which lies behind the 

 peristomium. There was no giant cell in the sixteenth 

 chsetigerous segment of this specimen. Griant cells are 

 not distinguishable in the small anterior tail segments, but 

 a few are present in the more posterior segments. One is 

 shown in the twelfth caudal segment. 



Fig. 53. Transverse section of the nerve cord of 

 Arenicola grubii. The section shows the dorsal fibrous 

 part of the cord, in the mid-dorsal region of which are 

 three giant fibres, the nuclei in the sheaths of which are 

 shown. In the ventral portion of the section note the 

 numerous small nerve cells, the nuclei of which are shown 

 on the right and left ; a bundle of pyriform ganglion cells 

 whose processes are directed into the fibrous part of the 

 cord ; and a giant nerve cell. The protoplasm of the latter 

 is reticulate and its nucleus vesicular. The cell gives off 

 a large process which, after sending branches into the 

 fibrous part of the cord, enters the right lateral giant fibre 

 at the point where there is a transverse connection between 

 the two lateral giant fibres. The neurofibrillse of the 

 process are shown. This drawing of the giant cell and its 

 process was obtained by superposing camera drawings of 

 the four consecutive sections in which these structures 

 occur, x 210. 



Fig. 54. Transverse section of nerve cord of Areni- 



