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vertebral segments. As development proceeded, the blind end 
of the most anterior of these became elongated, and gradually 
acquired a connection with each of the posterior tubes in suc- 
cession, and finally at its posterior extremity opened to the 
exterior. The author then entered into further details as to 
the changes which these parts subsequently underwent, and 
attempted to demonstrate the homologies between the kidneys 
of selachians and those of the higher vertebrates. 
He concluded by pointing out that the tubes he had de- 
scribed bore such a striking resemblance to the segmental 
organs of annelids that in his opinion the identity of the two 
structures was certain. It followed from this (1) that the 
ancestry of vertebrates was to be looked for in the annelids ; 
(2) that the vertebral segments of the vertebrates were to be 
looked upon as similar to those of annelids, and not, as had 
sometimes been said, as due to a secondary segmentation. 
