A STUDY OF METAMERISM. 415 



owing to the shifting of the metatneres, due to the introduc- 

 tion of an extra half-metamere, the halves of the 15th meta- 

 mere do not unite with one another. 



In fig. 34 two modifications of the inetameres are introduced 

 in front of the 15th metamere. Anteriorly the line between 

 the 4th and 5th metameres fails to meet above. The 7th 

 metamere is compound, so that an extra half-metamere is 

 introduced on one side (the left) ; nevertheless the two vasa 

 deferentia open on the same segment (16 — 15). 



In fig. 35, A,B,c, we find again two separate modifications. 

 A small half of the 3rd metamere forms above a union with 

 half of the same segment on the right side, and below it is 

 wedged in between the 2nd and 4th metameres. Again, further 

 back a half-segment is introduced on the left side between the 

 8th and 10th metameres (or, if the more anterior extra half be 

 counted, between the 9th and 10th). The openings of the vasa 

 deferentia were not made out, but the ovaries occurred in 

 consecutive segments, i. e. on the 13th half-metamere of each 

 side if the more anterior half-metamere (3rd) is not counted. 

 If this was counted, then the ovaries would lie in the 14th 

 half-metamere of the left side, and in the 13th half-metamere 

 of the right side. 



In fig. 36, A,B,c, a spiral ^ is introduced that involves the 11th, 

 12th, and 13th metameres, as shown in c. An extra half- 

 metamere (12th) is introduced on the right side. The open- 

 ings of the vasa deferentia were not seen, but dissection showed 

 that the ovaries are in consecutive segments. In the left 

 side the ovary occurred in the 14th half-metamere, and on the 

 right side in the 16th half-metamere. 



In fig. 37, A, B, the 12th metamere is compound, and we find 

 that the vasa deferentia open on correspondingly shifted meta- 

 meres. But, besides this, the openings of the right side of the 

 body have doubled, so that the 15th — 16th metamere has two 

 openings, right and left. 



In fig. 38, A, B, c (lateral), a half-metamere is introduced 

 between metameres 3 and 4. The openings of the vasa 

 * This case belongs to a preceding category, D. 



