A STUDY OF METAMERISM. 403 



II. Variations in the Position of the Reproductive 



Organs. 



With the hope of throwing additional light on the modifica- 

 tions in the arrangement of the metameres, I was led to 

 examine carefully those cases where the false arrangement 

 occurred in the segments anterior to the fifteenth. Here 

 there are definite landmarks, viz. on the outside are the 

 openings of the vasa deferentia, oviducts, and seminal re- 

 ceptacle, and on the inside are the organs belonging respectively 

 to these openings. The openings of the vasa deferentia on 

 the fifteenth segment are the only ones of these openings that 

 are readily and with certainty to be made out, so that I have 

 confined my study largely to the modifications in the position 

 of these openings. When we come to study the internal 

 arrangement of the organs, then the position of ovaries and 

 seminal receptacles will also be considered. 



In utilising the fifteenth segment as a point of departure, it 

 was first necessary to determine whether this was in reality a 

 fixed point. In a lot of 799 worms, twenty were found with 

 the vasa deferentia opening abnormally. In twelve cases of 

 the twenty the openings were on the same segment, but this 

 was not their normal segment (fifteenth). In six cases the 

 openings (right and left) were not on the same segment. In 

 two cases the openings were doubled on one side or the other. 

 To summarise : 



A. Openings on the same segment, but not on the 15th . 12 



B. Right and left openings, not on the same segment . 6 

 c. Openings doubled on one side . . . .2 



a. The following table records the openings of the vasa 

 deferentia in the first category. 



12 



