412 T. H. MOEGAN. 



recorded of such a modification, I think the latter interpreta- 

 tion is probably correct. 



In fig. 25; A, B, C; a rather complicated spiral involves the 10th, 

 11th, 12th, and 13th metameres, as shown in c. An additional 

 half-segment is introduced on the left side. Nevertheless both 

 of the openings of the vasa deferentia appear on the same seg- 

 ment (15th— 14th). 



Conclusions. — The number of worms recorded is too small 

 to give any conclusive data. In two cases (figs. 20, 21), where 

 an extra half segment is introduced, each opening of the vas 

 deferens is on its normal half-segment, and therefore on con- 

 secutive rings. 



In two other cases (figs. 22, 25) the openings of the vasa 

 deferentia occur on the same ring (14th — 15th in one case, 

 15th— 16th in the other). In a third case only one ovary was 

 found (fig. 23), and in a fourth the nature of the spiral was 

 doubtful. 



D. Figs. 26—32. 



Two kinds of modification belong to this category: 1st, 

 those where the spiral passes through the 15th metamere ; 

 and 2nd, those cases where the 15th metamere begins or ends 

 a spiral. 



1 st Case. — In fig. 26 is shown a dorsal view of a worm with 

 a spiral involving the 11th to the 24th metameres. The spiral 

 winds around the body thirteen times. The number of half- 

 segments is not increased by the spiral. Looking at the 

 lower surface of the worm the vasa deferentia are found on 

 the 15th metamere, and are in no way affected by the fact 

 that the metamere is part of a long spiral, and not a closed 



ring. 



In fig. 27, A, B, c, a spiral involves the 10th to the 16th meta- 

 meres. Looked at from below, b, the vasa deferentia are seen 

 on the 15th metamere. The reconstruction in c shows that 

 the 15th metamere is a part of the spiral, and still carries the 

 openings of the vasa deferentia. 



In fig. 28 a spiral is found involving the 13th to the 24th 



