A STUDY OF METAMERISM. 407 



opening on the left side of the 16th. The ovaries are found 

 in the 13th metamere (fig. 60^ a). 



No. 11, The paired openings of the vasa deferentia are 

 found on the 15th metamere. On the left side of the 14th 

 there is an additional opening. One pair of ovaries are found 

 in the 13th (fig. 60, b). 



No. 12. One case of doubling is recorded for L. terres- 

 tris (the preceding cases were all for L. foetidus) (fig. 74, 

 A, 74, b). The opening of the right vas deferens is doubled, and 

 opens both on the 15th and 16th metameres. The left only 

 appears on the 15th. Dissection showed both ovaries present 

 in the same segment and not doubled. The dissection shows 

 also the course taken by the vasa deferentia (fig. 74, b) ; and 

 we find a single vas deferens on the right side that supplies 

 both openings of that side. 



I regret that on account of the difficulty in dissecting out 

 the vasa deferentia in L. fcetida I did not get further evi- 

 dence as to the method of doubling of the external openings in 

 those worms. 



III. Abnormalities in Front of or including the 15th 



Somite. 



In a lot of 799 worms (L. foetidus), twenty, as recorded in 

 the preceding section, showed abnormalities in the position of 

 the openings of the vasa deferentia. In this same lot, after 

 the removal of these twenty (leaving 779), there were thirty- 

 two worms with abnormalities in front of or including the 

 15th metamere. This is in the proportion of 1 : 24. 



In 1893 I again collected material in order to obtain a 

 larger number of abnormalities in the anterior ends of the 

 worms. From 957 worms eighteen were found showing modifi- 

 cations of the anterior metameres. This is in the proportion 

 of 1 : 53. 



The material from these two sources, with a few additions 

 from other lots of worms, has been brought together and 

 figured in Pis. 41 and 42. 



VOL. 37, PART 4. — NEW^ SER. E E 



