A STUDY OP METAMEEISM. 41,7 



doubled on both sides. On the left side the openings are 

 found on the 15th and 16th half-metaraeres. On the right 

 side of the body the openings appear on the 20th and 21st 

 half-metaraeres. 



Infig. 45j A,B,c, we find the 6th metamere somewhat reduced 

 on the left side. We have an intercalated half-segment (15th) 

 on the right side, followed by a spiral involving the 15th to the 

 19th metaraeres. The latter introduces an extra half-metamere 

 on the right side. The openings of the vasa deferentia were 

 not found. Dissection showed the ovaries in the 18th half- 

 metamere of the left side, and in the 21st half-metamere of 

 the right side (in the half-metamere that follows the 18th on 

 the other side). 



In fig. 46, A, B, c, an extremely modified anterior end of a 

 worm is drawn. As the reconstruction shows, many extra 

 metameres are introduced on the left side of the body. In 

 the exterior of the 24th and 25th left half-metameres swollen 

 areas seem to point to openings of the vasa deferentia, but 

 none appear on the right side. In the dissection of this 

 worm no ovaries could be found, and no data throwing any 

 light on its '^ make-up" were obtained. 



Conclusion. — It is very difficult to reach any conclusion 

 in the face of so much conflicting evidence. It would seem 

 as though an intercalated segment might or might not affect 

 the position of the reproductive organs. If to get out of the 

 dilemma we assume that some of these cases are not due to 

 the intercalation of true half-metameres, but to unilateral 

 division of metameres, then other difficulties are encountered 

 as great or greater than those that appear on our first assump- 

 tion. It was only after the preceding pages were written and 

 the hopelessness of any explanation realised that a partial 

 solution — or what seems at first to be such — suggested itself 

 to me. Such cases as those drawn in figs. 41 and 46 might 

 be due to a regeneration in the adult of anterior meta- 

 meres. We see that this might offer an easy escape from 

 thedilemma. It seemed also to explain whythe segments in some 

 of these worms that carry the openings of the vasa deferentia 



