A STUDY OF METAMERISM. 433 



In a lot of 439 individuals there were found seventeen that 

 showed such variations. 



Benham (6) described in 1891 a variation in the openings of 

 the reproductive organs of Lumbricus herculeus. The vasa 

 deferentia appeared on the 14th and 15th metameres.^ 



With respect to the abnormal unions of metameres, and the 

 relation borne to the position of the reproductive organs^ there 

 is little to be added to the conclusions reached in the sections 

 dealing with abnormalities in front of or included in the 15th 

 metamere. Two cases were there sharply separated, — those 

 cases where there is a half-metamere more on one side than on 

 the other (C, second case, E), and those cases where the spiral 

 does not introduce an additional half-metaraere on one side 

 (B, C, first case, D). 



The results from the latter cases are in full harmony with 

 the interpretation of the spiral stated above. In those cases 

 where an additional half-metamere is introduced there are 

 certain examples that seem to verify the same statement ; but 

 there are otiier cases, and these form the majority, where the 

 results will not bear this interpretation. We have, then, to 

 assume, in some of the cases recorded, either that the half- 

 metameres are not equivalent to the normal, or else that the 

 reproductive organs do not give unfailing evidence of the 

 change that has taken place. Anyone who has studied the 

 facts will, I think, agree with me that it is far more probable 

 that the reproductive organs have appeared on a wrong (?) 

 half-metamere than that the half-blocks are not equivalent. 



This leads us to another side of the problem, as yet not 

 dealt with. It is natural to think of every half-block of one 

 side as having a half-block that belongs to it on the other 

 side ; in other words, to look upon one of these blocks as 

 predestined for the other, and we marvel to find them 

 separated. I think there are no real grounds for such an 



* Bateson's memoir, ' Materials for the Study of Variation,' that has just 

 reached me, refers to numerous cases of abnormalities in the reproductive 

 organs of earthworms recorded in a paper by Michaelsen, ' Jahrb. Hamb. 

 wiss. Auat.,' viii, 1891. I have not had access to this paper. 



