286 THEORIES ON THE ORIGIN OF VERTEBRATES 



That it had some relationship with Vertebrates was recognised 

 by Semper, Gegenbaur and others, but the full working-out 

 of its Vertebrate affinities is due to Bateson. 1 



Bateson broke completely with the Dohrn-Semper view 

 that the metamerism of Articulates and Vertebrates must be 

 put down to inheritance from a common ancestor. He held 

 that metamerism was merely a special manifestation of the 

 general property of repetition, common to all living things 

 (cf. Owen's " vegetative force "), and that accordingly " however 

 far back a segmented ancestor of a segmented descendant 

 may possibly be found, yet ultimately the form has still to 

 be sought for in which these repetitions had their origin " 

 (p. 549). The meaning of the phenomenon was obscure, 

 but he was convinced that the explanation was not 

 to be found in ancestry. " This much alone is clear," he 

 wrote, " that the meaning of cases of complex repetition 

 will not be found in the search for an ancestral form, which, 

 itself presenting this same character, may be twisted into 

 a representation of its supposed descendant. Such forms 

 there may be, but in finding them the real problem is not 

 even resolved a single stage ; for from whence was their 

 repetition derived? The answer to this question can only 

 come in a fuller understanding of the laws of growth and of 

 variation, which are as yet merely terms " (pp. 548-9). It 

 was in following up this line of thought that Bateson pro- 

 duced his monumental Materials for the Study of Variation 

 (1894). 



He found a strong positive argument for his theory that 

 Vertebfates are descended from unsegmented forms in the 

 fact that the notochord arises as an unsegmented structure. 

 With the notochord he homologised the supporting rod in 

 the proboscis of Balanoglossus^ which like the notochord 

 arises from the dorsal wall of the archcnteron, and has a 

 vacuolated structure. The gill-slits of Halanoglossns, with 

 their close resemblance in detail to those of Amphioxus, 

 Bateson also used as an argument in favour .of the phylo- 

 gcnetic relationship of the Entcropneusta and Vertebrata, 



1 In a scries of papers published in 1884-6, the speculative results 

 being discussed in his memoir on "The Ancestry of the Chordata," 

 Q.J.M.S. (n. s.), xxvi., pp. 535-71, 



