176 



Transnrtions 



In specimen A the pores went on for about 20 segments in regular altei'- 

 nation ; in specimen B the regularity is wanting, and the following table, 

 taken also from specimen B, shows the asymmetry of the pores on cither 

 side of the same segment. It gives the position of the pores in 14 segments 

 near the posterior end of the worm. 



Besides this alternation from segment to segment, there is an asymmetry 

 on the right and left sides of the same segment — i.e., a segment may have 

 a dorsal pore on the right side and a ventral 

 pore on the left, and vice versa. This, however, 

 is not invariable, though it is frequent. In 

 some specimens examined the dorsal pore of the 

 right-hand side was found more often oppo- 

 site a dorsal on the left hand than opposite a 

 ventral. In tlie majority of the worms ex- 

 amined, however, the asymmetry occurs. 



In the first six nephridial-bearing segments 

 the nephridiopores are in one and the same 

 line— I.e., they occupy the dorsal position on 

 both right and left sides. In some cases the 

 i th of those segments was reached before any 

 alternation commenced. A similar fact was 

 noted by Benham (12) in M. uliginosus. But. 

 excluding these anterior segments, there are 

 more pores placed dorsally throughout the 

 length of the worm (which contains about 170 

 Segments) than ventral ly. It may here be 

 noted that in the table given by Borelli (13) of 

 the position of the nephridiopores in various 

 species of the European genera AUolohophora 

 and Lxmhricus there are, on the whole, fewer 

 porfs in the dorsal than in the ventral positions. 



Fig. 1. 

 Anterior v.nd of jV. rosae (pre- 

 served in alcohol after po- 

 tassir- bichromate and acetic 

 acid), showmg the po,sition 

 of the anterior nephridio- 

 pove.-i. the first of which 

 (n.p.) lies in line with the 

 prostoniial furrow. 



