TTTBIFEX. 337 



placed longitudinally. There is a single ganglion 

 situated near the posterior border of each segment, and 

 these are connected into a continuous chain by a series of 

 connectives which unite adjacent ganglia. In the 

 anterior segments the ganglion and connective are about 

 equal in length, the connective, if anything, being a little 

 longer. More posteriorly, however, where the segments 

 become shorter, the proportions of these two parts of the 

 nerve cord also change. The connectives become shorter 

 and shorter, but the ganglia change very little in size, 

 so that, finally, the connectives are extremely short, and 

 the ganglion occupies almost the whole length of the 

 segment. But throughout the length of the nerve cord 

 the two parts are sharply marked off from one another. 

 This is very clearly seen if one examines the living worm, 

 but when the nerve cord is seen in section the difference 

 between the two is even more apparent. The connective 

 is of about the same diameter throughout its length, but 

 the diameter of the ganglion varies in different parts. In 

 most cases it can clearly be divided into three lobes placed 

 end to end and separated from one another by constric- 

 tions. Of these lobes, the first is the largest, while the 

 other two are of nearly the same size, the posterior one 

 being very slightly smaller. 



The ventral nerve cord gives off branches or 

 peripheral nerves in each segment. There has been a 

 considerable difference of opinion amongst earlier 

 authorities as to the number of these branches in each 

 segment. Vejdovsky (1884) figures no fewer than five 

 pairs; D'Udekem (1855) states that there are three 

 pairs, but Nasse (1882) was only able to find two. After 

 careful examination of the living worm and sections, 

 I have come to the conclusion that there are three pairs 

 of these lateral nerves in each segment. Their places of 



