No. 2.] SPIRAL MODIFICATION OF METAMERISM. 25 1 



of Oligochaeta, and also in many different genera of Polychaetous 

 Annelids. Whatever, therefore, be the cause of the phenomena, 

 it must be a very fundamental one. 



My work is still in progress, and I reserve for the future a 

 fuller discussion and a more extended account of these occur- 

 rences. There are a few general considerations that have grown 

 out of the work that I find full of suggestion, and as such I 

 offer them here. 



1. A very similar splitting (but not the spiral) has been 

 described and figured for the Cestodes. I have also seen these. 

 The occurrences of such similar processes of growth in both 

 Cestodes and Annelids suggests that metamerism in the two 

 groups has the same fundamental (though not phylogenetic) 

 explanation. 



2. On the conventional assumption that metamerism in the 

 Annelids is to be explained by a theory of budding, it seems 

 evident from the facts outlined above that the right and left 

 sides may bud independently. This leads to the improbable 

 conception that the Annelid is formed of two parallel rows of 

 buds, and that a single worm may have more of these buds on 

 one side than on the other. 



3. The conversion of the opposite arrangement of metameric 

 blocks into the alternate producing the spiral finds its explana- 

 tion in the relative size and position of the blocks of the two 

 sides. Similarly in plants, the arrangement of the leaves into 

 opposite, alternate, or spiral finds its explanation in the pack- 

 ing of the leaves in the bud ; and the transition from the one 

 method to the other, often in the same plants, is explained by 

 processes of cell growth. This may indicate that a fundamental 

 interpretation may be found for both. 



The Marine Laboratory, 



Wood's Holl, Mass., 

 August 22, 1892. 



