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THE ANCESTRY OF THE CHORDATA. 53 
The Ancestry of the Chordata. 
By 
William Bateson, M.A., 
Fellow of St. John’s College, Cambridge. 
Tue ANCESTRY OF THE CHORDATA. 
Preface.—In view of the facts relating to the structure of 
the Enteropneusta which form the subject of the accom- 
panying paper and of those which have preceded it, it seemed 
necessary to attempt some analysis of their import and bearing 
upon morphological problems, and especially upon the vexed 
question of the ancestry of the Chordata. 
But at the outset it was impossible to attempt such an 
analysis without first clearing the way by a discussion of the 
morphologic meaning of Segmentation. Since the Enterop- 
neusta are essentially “ unsegmented ” animals and the Verte- 
brata are ‘‘ segmented,” this preliminary discussion was neces- 
sary. Moreover, having shown reason for not accepting the 
view that the vertebrate segmentation was of such a kind as to 
necessitate the existence of a series of segmented ancestors to 
account for it, it became also necessary to treat the whole 
question of the origin of segmentations of this class upon a 
wider basis. This must be the apology for the introduction 
into this paper of some matter and speculation not otherwise 
immediately relevant to the subject. 
The decision that it would be profitable to analyse the 
bearing of the new fact in the light of modern methods of 
morphological criticism, does not in any way prejudge the 
question as to the possible or even probable error in these 
methods. 
Of late the attempt to arrange genealogical trees involving 
